Aibu for thinking this is a little weird?

Absolutely.
Czech citizen here.

If your DD had never had a friend to the house before then it’s possible hers hasn’t, either, I think she’s just misunderstood rather than it being “weird”, and thought this was a social invitation. Unless it’s clearly communicated there’s no easy way for either party to clarify after arrival: you felt too awkward to say anything, if she said after a while “shall I leave now?” she’d probably worry that you’d interpret that as “I am bored of talking to you.” Just make sure it’s clear in future.

Staying for play dates never happened when I was a lass, nor when I had my children. It was usually greet at the door, invited child runs inside, parents negotiate a pick up or drop off time still at the door.

If it's the first time they have been round I'd want to come in for a bit and scope out the environment (any big dogs etc.). I'd be ok leaving after a cup of tea if the girls were settled though at 8. I have always had the parents stay so far for my daughter though as she is only 5 and that's just too little for me just yet.

My advice would be from much experience
don’t bother with home visits and other mothers and children’s friends .. it never works out

Thats so weird, because ive just seen another post from a Polish mother who had taken her 8 year old to a play date and was annoyed that she was expected to stay for the whole 5 hours when she had her own shit to be getting on with.

I really think it depends, I’ve gone to play dates whereby I’ve been invited in for a cup of tea so ended up staying, others whereby I dropped off dc and went on my merry way. Definitely just a misunderstanding / different ways of doing things. Maybe she didn’t feel comfortable leaving her child with a parent she didn’t really know! Next time just make it clear to drop off and be back at such and such a time to pick up.

If you don’t know the mum then would you send your child round to theirs? Personally unless I knew the parents my kids would not be going for play dates unless I was there 🤷🏼‍♀️

After 2 hours or so I would have said to the mum ‘relax with a cup of tea. I’m just going to put a wash on/hoover in the other room/load the dishwasher’ or whatever needed doing.

Some people do one or the other, or both. Depending on age and parents’ wishes.

Unfortunate miscommunication and a bit awkward but it’s done now.

They might if its the first time they met you.

8 with friends from school? I think most people in our class didn’t stay at parties from about Year 2 onwards. I’d say most playdates are without parents from 5 onwards. If someone invites your child over from school at 8, I dont think they are expecting you to stay.

I don't think it's weird that the mum stayed. You say you have never spoken to the mum before. She doesn't know you. I think it's very wise to check out a family you don't know rather than just dumping your kid. I don't know why people feel so safe leaving their child with a complete stranger just because they are a parent.

At 8 years old there is no way for them to contact you if anything is wrong as it's unlikely an 8 year old will have a phone.

I had this when the kids were young (also Mum is the same nationality) so I think it is most likely a difference in culture. Playdate at someones house in the UK generally means dropping off (unless the kids are very young (toddlers) and then its obvious you would stay). Once they are school age, its usually parents taking turns to have the kids and just as you said, they can play and Mum/Dad can get stuff done.

I would just make it very clear next time in the message - ‘Would your daughter like to come round to play? I’ll just be doing housework/work and they can happily play together. Happy to feed xxx and drop her back afterwards to you’.

I wouldnt leave an 8year old in a strange house with parents id never met before. I think its normal to stay although id have expected to only be there like 2 hrs

This

First play dates usually involve parents if they don’t know you. They wouldn’t leave their kid with a stranger they don’t really know anything about.

At 8 years old a drop off is fine, but only with someone you know. Would you really drop your daughter off at the house of a virtual stranger you’d never spoken to, not knowing if the house was safe, who else (eg adult males) might be there? To me it’s weird you expected her to drop her daughter off without knowing you or your house?

Did you specify an end time? Usually the sentence "you can drop her off at this time and pick her up at 5 /we'll drop her off at 5" solves the potential misunderstanding/confusion.

I wouldn't expect them to stay. I'd make it clear she could drop off and pick up at certain times though. Maybe she misunderstood.

In many European cultures when you invite a kid for a play date, especially if the parents do not know each other, you stay over, to ensure things get on smoothly. It would also be considered rude to drop off as wanting free babysitting. You only drop off if you know the parents very well. Play dates (and birthdays) last not 2 hour but the whole afternoon. Additionally she might not have many friends in the uk or in that school and she might have seen this as an opportunity to have a chat. Obviously it was a difficult chat as you were not interested in knowing her and only wanted to get on with your things. She might have felt uncomfortable and making an extra effort to stay longer and to talk to you and try and understand your English (do you have a thick regional accent?) not to be rude. That’s why British people are considered cold and unapproachable (and rude) by Europeans.
do not worry by the time her second child is in primary she would have gotten all these unwritten rules and will be dropping off her kids without attempting any social approach to any of the parents who she will get the cues are not interested in her.

I think it is in how you invite them. Close friends of my DC we often go over each others and have a cup of tea whike kids play, this is very normal. However as they have got older / we need to get things done we just clearly invite the child and suggest a time for pick up.

If the friend been to your house before then yes I would have expected her to be left but as the woman didn’t really know you then I don’t think that’s unreasonable. I am at a loss to understand though how the conversation went did you not say “yes drop friend over at 2 and then can you come and collect her at whatever’ ? this would have given her the opportunity to say that she’d rather stay with her

So the mum and the little sister stayed? So 2 extra?

Sounds like miscommunication, but surely you could have made your excuses after a couple of hours?