I set a schedule with my 5yo.
We go to the park with classmates on Monday, on Tuesday and Wednesday we have down days (with the option every two weeks or so of meeting up with some old playmates, who I contact), Thursday is music class and Friday swimming.
We have no plans for the weekend, so we can travel around and visit - or just catch up with chores, shop and cook stew for the week!
Recently, DD has started whining and sulking if she doesn't get her way - and I suspect that someone in her class does it and she's trying it out. She throws strops as well - chucking her coat down on the floor etc.... Give me strength. I take a very dim view of sulking and strops.
So, I have to take a deep breath and remember that she's just started school, and that it's stressful for her: her teacher has a different style to us - she punishes for bad behaviour (no play time, naughty step etc) - which we never did, as we always emphasised discipline and teamwork rather than threats, punishments and exclusions.
I really find the sulking and strops very tiring. I hope it's just a phase - and she's copying someone??!!
I wouldn't let a 4yo go alone to a playdate TBH. If only for the reason of not wanting a 4yo friend coming round to ours - we don't have the space - and IMHE they get wild when they're together.. better to meet where they can let off steam.
It's all a work in progress isn't it? Setting boundaries, being consistent, and trying to get them on-side. Here's hoping!