Nanny has offered free childcare

Just say no.

I had a nanny try to do this, to effectively use my house as a base for childminding a much younger child in my home. I said no, she’s employees to look after my DC and that my home wasn’t baby proofed. Turns out the other parent had been told that I was fine with it! I hadn’t been asked and found out by chance

I used to be a nanny.

If she's employed then you should have been asked and are within your rights to ask her not to do it. She may well be getting paid but she may also just be trying to facilitate a play date.

If she's self employed and you don't pay her tax then she can do this and even be paid by the other family however she should get your permission if the child is coming to your house so she should pick the other child up on the way to the outing.

Tell the nanny she needs to sort out separate insurance for this as it's not covered by yours and you're taking no personal responsibility as the parents haven't even discussed it with you.
What a bunch of cheeky fuckers! Both the nanny and the parents.

Did you say any of this to your nanny at the time? It would be a no from me.

4 kids.

I would have a word with the nanny about making plans without consulting you first because she massively overstepped. However, additional 8 year old might actually make the adventure park easier as your eldest will be entertained and they can probably go on rides together without an adult leaving the nanny to focus on the younger 2. Just don’t be shy about asking the parents to transfer you the cost of the ticket and to provide a packed lunch and/or spending money. I don’t see how Monday can possibly cost you extra petrol and is an extra child portion of dinner really significant, especially given you’d hope the other family will reciprocate at some point. Again, it’ll be fun company for the older one so the nanny will have more attention for the youngest. I’d let it go this time but would definitely speak to the nanny. Don’t give her notice though, you risk getting screwed over the summer holidays if she leaves early for another job.

This.

If she is looking after another child then you can renegotiate costs. Is there insurance for this and them being in your house if there’s an accident?

You need to tell her it can’t happen and her response will tell you what you should do come September.

Tell your nanny and be upfront.

I've heard that you have apparently made arrangements for X to come here so that you can look after him. I am not happy about this and you need to cancel these plans, as our agreement is that during your working hours with me you are only looking after my children. If you want to look after other people's children during your working hours with me, then you need to OK it with me first - but unless there is a really good reason for you asking, I will most likely say no.

If the invited child is a friend of your DC, surely they have been invited so your DC can socialise and have more fun? I would personally encourage this because children need to develop friendships, and sharing days out would be the perfect way to do this.

Additionally, the other child's family may reciprocate by inviting your child.

Have you asked your DC what they think of the arrangement? Maybe the children thought it up between them and your nanny facilitated it for them.

I am surprised by how many people think this is unreasonable.

Wtf? I think you need to point out to your nanny that she’s literally at work. You’re paying her to look after your children, not someone else’s! She doesn’t get to invite her mates kids round

The extra child might actually make an adventure park easier, logistically. I'd be more comfortable with two eight year olds on rides together without me than one eight year old alone, and otherwise eight year old can only go on rides suitable for the youngest which is a bit rubbish for them.

This would be my concern!!

Why are you assuming you will be paying additional costs? Surely the fuel is the same regardless, and for all you know Nanny is receiving the child's entry fee from the other parent.

And why would you have to feed the child?

Oh, sorry, I think that takes the total to 4 kids.

But I still wouldn’t be happy. Especially not with a 2 year old in the mix.

Is she an experienced Nanny? As in has taken on other long term jobs before? Surely she knows this is not ok without asking you?

For me, it’s not the money, it’s the spreading more thinly the responsibility she can take for each child. And the principle of you paying for childcare for two days for friend’s parents!

Sorry typo, 4 kids. Still would be a no from me.

Just tell her you are not comfortable with that and to cancel. I doubt the other family is not paying her extra tbh.

YANBU. How did you find out? I would not be okay with this, especially as she will have to look after 5 kids in an adventure park.

There is no way I would be happy for my Nanny to have responsibility for 5 kids on a trip out / adventure park, especially when the youngest is only 2!

Just tell your Nanny that you do not agree to her looking after other kids or doing childcare for others while she has responsibility for your children.

Are you certain you will be expected to cover additional costs?

It's one thing for the other parents to feel it's okay for your nanny to look after one extra child for no cost for a couple of days (it's not) but ludicrous for them to not expect to have to cover the cost of outings.

But I also would be unhappy with one adult taking 4 young children out and about.

The other thing I’d add is that, as a parent, I’ve noticed that different nannies have different relationships/arrangements with the families they work for. My children have sometimes been directly invited by the nanny, other times it’s by the mother who’ll then say “my nanny will be looking after them”. So the parents may not have thought it necessary to speak to you directly if they thought your nanny had the autonomy to do that. (Mind you - I hate to say it - but I bet the pp upthread is right that they’ve offered her cash in hand and nobody has thought through the fact that everyone is essentially ripping you off royally in the process…..)

You don’t have to give extra money just give for your own dc for the days out !

Whilst she may not be being paid 'officially' I suspect your nanny will be expecting a nice gift/a token about to 'happen' to be given her to her after the couple of days. I would not be happy about this at all - play dates for a few hours yes but her unilaterally organising to take another child for two full days and for you to foot the bill for costs associate with this is ridiculous.

the parents haven't even had the decency to check with me that this is OK or offer to share costs.

Do the other parents actually know that you were unaware about the arrangement? If the nanny has invited the child (as per your OP) then they may have assumed you knew, and the nanny could have discussed additional costs etc with them. They may have already given her money for their child to attend the days out, or she may have told them not to worry.

I didn’t think about the other family paying her…..! The theme park thing is a decent get out, actually - as I’m not sure I’d be happy with only one adult and four kids in that scenario. Odd number makes it difficult on rides, for example - and many require an adult to go on too. I think you could quite easily get away with a “not comfortable to take on that sort of responsibility” approach. As others have said, it’s a different kettle of fish from a play date one afternoon.

Sorry you AIBU was about giving notice. It's harder to cope with wrap around care at school but it sounds like your relationship is probably at an end so if tell her she finished after the summer hols