To think our house is making DC sick

That's nasty, OP. We have black mould (but not to that extent) and use black mould remover - it's the only product that works for us.
However, ventilation is the key. I don't know how old the property is, but ours is an old stone house. Old properties had sash windows for that reason - to let the air flow.
Not good for your little one (or any of you) to be breathing it in, and you absolutely should be taken seriously.

I'm.ashamed to say my house is bad with mould too and all these comments kicked my ass today to do something about it. So I've had all the windows open and treated it with kilrock mould remover the best stuff ever. Half an hour wipe off and it's gone. Need to ventilate though because it's very bleachy . I hope u read this and it helps you

You need to get your family out of there.

A little boy died not long ago from black mould.

If it was me, I’d be working every hour I could to get my family out of there & I certainly wouldn’t be bringing a new baby into the situation. You need to help yourself.

I'm so sorry you are going through this- my family and I have recently gone through a similar situation- we lived in a council property for 13 years- the last years were hell- we had black mould covering the whole bathroom and in my children's rooms- we complained numerous times- had treatments to the walls etc but kept coming back. My youngest was ill ALL the time, constant colds, random temperatures, just constantly- I wasn't sure if it was the house as he was poorly as a newborn so put it down to poor immune system. Anyway long story short- it was rising damp- the council had to permanently move us in order to carry out the work required- needless to say since living in our new house my son hasn't been ill! Not so much as a sniffle!
Can't you go to your local council for help?

OP, you need a plan to get out of there pronto.

Why, after 5 years are you still there?
How low is your joint income?
Can you move further away?

There has to be better options than remaining in that house?
Who are you living with that thinks this is ok?

If you explain your circumstances, maybe MN can come up with a plan?

In the imeadate term, open windows daily, heat rooms daily, don't dry clothes inside unless in a closed room with dehumidifier, buy a dehumidifier for each room you sleep in, wipe mould daily, hire a carpet cleaner, buy the dessicated dehumidifiers too.

Do you have any dehumidifiers? I lived in a horrendously damp and mouldy house with my partner and child for 3.5 years, we were desperate to move but it took us that long to find somewhere else we could afford to rent. We had 2 dehumidifiers going, one upstairs, one down, and moved them around. Found one of them cheaply on FB marketplace but spent extra on getting the other one new. Also found a cheap air purifier on ebay and used that as well. We're now in a damp and mould free house thank god but I kept the good dehumidifier and use it to dry washing which also helps to prevent damp. This is the dehumidifier we have - https://www.vonhaus.com/vh_en/12l-dehumidifier-vonhaus - and the air purifier, which you could have in your child's bedroom, is a fairly old HoMedics AR10 with HEPA filter and it works fine but is a bit noisy. I really recommend spending the money on these if you possibly can as you seem to be stuck in that situation for the forseeable.

I grew up in a home built from 1830’s, we had no radiators in bedrooms, single glazing and frost inside the windows in the morning. I developed eczema which goes hand in hand with asthma. I then developed severe asthma (I’m talking multiple icu admissions). I don’t remember mould as a child but I guess it was there.
I moved in my 20’s and suddenly I have no more asthma attacks, despite not being compliant with my medication.

Aged 30 I was diagnosed with MS - autoimmune Illness.

I then moved home again 3 years ago while we built our house - the eczema returned, surprise! We’ve since moved into our new home and the eczema has settled down, with using no ointments.

It’s home and such a beautiful house but it is riddled with Damp and mould - no matter how much scrubbing I did. We had a baby and treated our bedroom with a sort of mould paint, It certainly helped. I also used astonish mould and mildew.

I don’t have any advice but please know that you are right to be concerned about your daughter, please keep doing what you’re doing and move out the second the opportunity arises. Keep asking the Dr for referrals for allergy testing, if they won’t do it go to another doctor, and another and another. perhaps consider having a done privately - I promise you, it’s an investment in your daughter’s future.

You need to get out..black mold can cause autoimmune issues, that doesn't look good. Do whatever you can

@WorriedRelative I just don't get why Awaab's Law (that poor little boy) only applies to social housing tenants?
Why don't private rental tenants matter?

The plan is to extend Awaab's law to cover private rentals in due course.

@Concernedmum23 buy mould remover and clean it. Get a small tin of special mould paint and apply over the cleaned area. (Not sure about the carpets). Open the bedroom window for at least 15 mins every morning. Do not dry washing on the radiators, at least in the bedroom. My granddaughter is like this too, especially nursery term. I'd take her to the doctor as well.

Well it looks like another thread abandoned by an OP! Anyone else getting fed up of these?!

@Concernedmum23 what you can do and apologise if you have but ask to get her tested for allergies at the hospital then you will know

We lived in a damp house that we have since demolished and rebuilt on the plot. When we demolished we discovered there was no damp proof course. My DS had all sorts of allergies - snuffled/ sniffed permanently, runny nose etc. As soon as we moved out he improved and now we are in the new house, he’s a different child.

@asrl78 If it's a private rental (not sure if it is), it is so much harder to get the landlord to do anything. It is shocking that they aren't "covered by laws" in the same way as social housing is, but they never have been.
We're long-term private renters as, despite both working our arses off, we simply can't afford to buy. Been renting around a decade now.
My first rental property (a single mum at the time) was full of mould. Landlord did nothing because realistically he didn't "have" to. Kept saying he would get the problem sorted but never did.
I saved bloody hard so we could move to a more suitable property.
The place we are in now isn't mouldy, it's lovely in fact, but again the Landlady does naff all. We replaced the broken toilet seats ourselves, for example.when we moved in, as didn't want the toddler hurting herself. The guttering still leaks which ultimately is going to cause issues down the line but we've told her and nothing.
But the main thing for us is that the house is safe for our kids. That's the responsibility of a parent.

Why are you and dh bringing another child into this environment when you suspect it's making your dc ill and you have no hope of moving out in the near future?

That is one of the landlord's responsibities, to fix structural-related problems like that, it is why the tenants are paying him rent that is considerably above the landlord's mortgage repayment.

This is so easy to fix. You have negative air flow inside therefore the wet air that you breathe out is trapped and is attracted to the coolness of the walls where it collects and molds.
you need to increase air flow open all windows for 10 mins a day to allow the air to exchange.
a long term fix is a positive input ventilation system - not stupidly expensive (£300-£500 depending on property size) and super easy to install for a competent diyer

"I don't understand why they shut you down when you mention it!"

I can think of one reason, classic denial response. Some people think that denying and ignoring uncomfortable realities will magically make them go away. It doesn't, but what it can and often does do is make those realities harder to address and makes things worse in the long run.

Exposure to mould and damp makes me very ill, instant asthma and sneezing. I lived in a property that was very damp for about a year. It took a while with dr to figure out what was going on as I thought I was getting flu all the time and having to take so much time off work - then she figured out all my symptoms were an allergy to damp spores. Started taking high dose anti-histamines along with asthma/respiratory stuff and it is manageable if I find myself in a damp environment. But I avoid if possible.

I haven't read the entire thread so apologies if I'm repeating stuff.

For the mould I recommend HG mould remover spray https://amzn.eu/d/b3GhdpM and a plug in dehumidifier (much more effective than the pots). You will need to keep cleaning it off regularly since the cause is not going to be addressed.

Just because you can see mould it doesn't mean that is the cause. Similar symptoms in my DC have been caused by low iron in one and gluten intolerance in another. The gluten intolerance symptoms cleared very quickly once we put the child on a gluten free diet so that's quite an easy one to try for a couple of weeks and see if it helps. Iron levels can be checked via the GP.

@Porcuporpoise have you seen the pictures OP has shared? Of course it’s the mold. No child should have to live inhaling those spores day in and day out. She may never recover from the damage it’s already done to her and they are about to make a tiny newborn baby live there.

It could be the mold and an dehumidifier is an excellent idea but it could also be plain old allergy if they have animals. The dark circles under the eyes are a really common sign of allergic load.
But as you can't move there's little to be done about it. You could speak to a doctor and try a regular antihistamine, or buy an air purifier and try that in her bedroom (and don't let the animals in).