All 4 of us to attend bday party?

It's very area and parent culture dependent. At my DDs nursery parties the first couple of parties had most of the first time parents having both parents attending. The parents with elder siblings tended to just send 1 parent. These were all at big venues like soft play/ play cafe. After about party 3 it moved to pretty much everyone doing 1 parent per child.

At someone's house (regardless of how many other parties have been held) it's 1 parent per child. At soft play/ leisure centre/ play cafe some parents will attend together, especially if siblings are welcome and can be paid in. Although a lot of the time it's mum/ Dad with the kids whilst other parent stops home and cracks on with jobs.

one go in and do drop off, introduce yourself to the parents etc, leave then the other do pick up, introduce themself to the parents.

I love that some of the answers now are "It's fine if the hosts are wealthy."

OP, I would just ask. "DD would love to come - do you mind if all of us come along as it would be nice to see DD socialising with her little friends and we can help out if you need it?"

It’s weird to want to make a random child’s birthday party your weekend family outing. Do something as a family later or the next day.

I wouldn't all turn up. One of you go and either message the other one if it's clear other entire families have turned up / it's in the garden so there is definitely space. Or make up an appointment or class or something and swap half way throigh if you both want to use it as an opportunity to meet people

Definitely not the done thing.

Surely it’s max 2-3 hours, you have the rest of the weekend to do things as a family.

That’s overwhelming not likely to happen though. It will likely be 2-3 dads at most.

Very much this! It’s not a family outing.

DH and I always went to parties as a 4, because we had twins.

I’m generally pretty laid back about the 2 parent thing (unlike most of Mumsnet who liken it to trailing dog poo through someone’s house), however I think it’s a bit off to view it as a family outing – it’s not, it’s someone else’s party.

But if you invite 10 children and then find that you have 30 people plus 10 babes in arms attending, that’s potentially overwhelming.

Depends on demographic. If you are in a wealthier demographic this is completely normal.

Even at a leisure centre there can be limited space. The accepted rule is one parent only and no siblings unless this has been agreed and you don’t have another parent at home.
My nephew had a family that came as a 4 to his son’s birthday. They were talked about, especially as the sibling was an older child who was a pain in the neck.

Ask when you reply.
There really is a lot of variation.
It might be that they want to meet other families too.

I would allocate your husband to take D2.
Taking a newborn out to socialise before having some vaccination shots is a risk.

The party is for the birthday child you meeting potential parent friends is a bonus. Don’t crash a child’s birthday for your on family needs.

At the very least you need to ask.

I had a party for one of my kids when he was around 5 and it was at my very small house. One friend messaged and said could she bring her son's siblings and I said I was really sorry but we were limited on space but that if she couldn't get childcare I'd rather have them all than none of them and we'd squish in.

She got childcare, so it was all good.
And then on the day of the party one little boy arrives with mum and dad and baby sibling. Like... wtf?
They didn't even ask, just sat down taking up the entire sofa and made themselves at home. I felt really awkward, especially because I was worried my friend then felt like I'd been unfair and asked her not to bring siblings but let other people do so.

Anyway, that's a really long way to say don't do it.

This actually reminds me of a party my DD went to when she was in year 1. COVID had meant they weren't in for reception so this was the first time people began to host parties. She was invited to a party at someone's house and on arrival the mum politely said parents are welcome to stay...which everyone did (it was a September birthday so probably the first school party and no one wanted to leave their 5 year old at a strangers house).
Afterwards I did hear the mum saying she didn't realise everyone would stay, that it was more chaotic than she expected as she ended up trying to host parents and children (plus it was a very small house so with 10 parents it was a bit of a squeeze). She made sure the following year to include drop and go on the invite 😂

Another Londoner here who thinks this is very common. Unless it soft play, or somewhere with an entry charge the parents have paid, the whole family goes. They are social events at our school. The children all play together and the parents hang out and chat. We have a lovely community of parents and getting to know them makes it easier for play dates etc.

As the information isn’t explicit, and you’re not sure what the etiquette is where you are, I’d text the organiser and ask if the invite is for child plus parent or everyone, making it clear either option is fine for you.

I don't recognise this idea of parties being hellish endurance tests either. They were always for us a nice afternoon for the children to be entertained while the adults had a catch-up. Neither DH or I saw making friends or having normal social interaction as the terrible chore it is being made out to be.

No, don't do it.
For one for the space issue, Another as all the attention will be off the birthday child and onto your baby, which isn't fair.

No, not at someone’s house. Either Dh goes or you go with the baby. Bringing the baby would be fine, but just mention it in your rsvp.

At soft play, totally fine as long as you pay for yourself, though a bit weird. There are always a few of those couples who can’t seem to be out of each other’s sight. We all know who they are. They’re the ones who seem to do the school run together every day. But honestly, birthday parties are for whoever draws the short straw. No one actually wants to go to them. One of you goes because you have to.

If you do go to a venue party though, offer to pay for the extra parent. We’ve definitely done parties, like for our 10 year old, where we didn’t expect parents to come and suddenly they both turn up and it’s £15 per person for entry and they just stood there at the door to be counted while we paid. 🙄 I would have been out of there like a shot to have a coffee in peace at the cafe.

Well, I’m a Londoner too who thinks this is absolutely not fine 🤷🏻‍♀️
What do you normally do at the weekends, op, if you think going to a stranger’s house would be a “nice , family thing to do”?

I did a house party for my daughter's 5th birthday and made it clear parents could stay if they wanted but space was limited so drop and go also fine. EVERY adult stayed and the living room dining room was flanked with parents standing shoulder to shoulder. One parent was tasked with making brews for everyone and the whole thing just felt like a spectator sport of trying to entertain children and do party games while their parents stared from the sidelines in an enclosed space. Hard work!

It’s not a nice family thing for all four of you though, the invitation was for your toddler and who naturally needs someone to take them.

I have felt like this - would always view party attendance as a one of the team job and I struggle to understand why a couple would both want to do this. But op your opening post is sweet and you are both right to think about socialising with nursery parents and building your network. This just isn’t the place for that imo.

Assuming this is a normal house- it is likely already pretty full to bursting with the people they have invited and their family members. We always went just one parent and alternated and it was often hard for people to find seats even then. For a village hall party, it is usually fine for you both to go (just ask first).

For my daughters reception party we did have a few parents ask to both join, and we agree and it was nice to chat to them, but I'm not sure they realised we had to pay extra (£10 each) for the second parents to the venue than we had originally budgeted.

If you live in a very affluent area and they have a very large house you would probably be fine to ask to both join as space would likely be less of an issue.