Teach me about 'playing out' and going to friends houses!

[again2020]

We live on a friendly, kid friendly estate with a little park and some fields and walking paths nearby.
It can be quite a busy area.
DD is now nearly 4 and a half, and often sees the local children on the park and going around on their bikes. Some of these children go to her school, some don't, and several are older at 5,6 or 7. She always wants to go out to play with them and I take her almost every time..I'm probably over compensating for her being an only child there.
The children seem very nice but often they are playing on the park alone or riding there bikes on the quiet roads for up to an hour or so without their parents. Is this normal? (Aged 4-7 children).
The park is behind the houses and can be seen from some households windows, but not all.
I'm often the only adult there and as a result children have asked to come back to our house to play with DD. I did let a little girl come once for a drink for 10 minutes or so. I didn't know where she lived at the time so couldn't knock on her parents house.
I've since spoken to her mum and she is nice. Tonight it happened again where 2 girls wanted to come back and I made an excuse and said I'd watch them on their bikes for a while but they couldn't come round tonight, maybe another time.
What are thoughts on this? I'm happy DD has made friends but I'm an introvert with an extroverted child and find it hard to have an 'open door' policy. I grew up in a household where I wasn't allowed friends in and I hated it and wouldn't want that for DD, but this is new to me so any advice is welcome. If I knew their parents better I'd feel better about them coming round and I prefer some notice so I can prepare. Is that old fashioned?

Firstly, no child should really be in your house without the parent's knowledge, in my opinion, unless they are friends and it's a regular thing that they just pop over, but then in that scenario I would have the parents number and txt saying "x is in ours if you need her"

And also, if you are not comfortable with it, just do as you are and say "not today, where do you live, I will come and speak to who's at home and we can arrange it for Monday "
I think if your daughters an extrovert it's not bad to feed that once in a while.

Oh and you sound like a lovely mum by the way

@Thinkbiglittleone Thank you!

I wouldn't like my DD going to people's homes without me knowing but I find the lack of parents quite strange. Hopefully I'll get to know the parents better soon.

We have kids that play out here from school age. I don't let my Ds out unsupervised, but I am starting to feel a little more confident about say nipping in for a second to get something ( he's nearly 6)! I just worry about him running in front of a car as he often doesn't look ( despite endless reminding.)

I would say generally it's more of a working class thing to let your children play out unsupervised and that sadly middle class parents either just don't let them out or it's supervised.

I see kids walking home alone from junior school here ( maybe age 9/10) and it makes me edgy, but i might feel different by the time my Dc are older. I suppose you have to give them some independence gradually before they get to secondary school at 11 years old.