The one thing, or really one of many things, people do not prep you for in parenthood is the ever elvoving play date. Play dates are often amazing. At this point in the game we only make plans with people we all like. Meaning I don't make plans with rude moms. You see when you start in the play date world you just make plans with anyone your kid gets along with...but it only takes a short while to realize that while kids play the parents must talk with each other. At this point I generally have a lovely time with my mother friends, but this is after years of experience and some more awkward play dates. Nothing terrible, but it can be hard to make small talk for a couple of hours---so nice to have a connection.
Now play dates tend to have some unspoken rules:
1) Take care of your own. Bring food, snacks, wet wipes, towels or whatever. In my experience the other mothers are always far more prepared than I. We all live so I don't sweat it.
2) Agree on a time and place, but be flexible. Things happen....puke, allergies, random issues. Rescheduled play dates are common.
3) Two hours. An unspoken two hours is standard. Don't be that mom who stays for five hours. We all have other stuff to do.
4) Drop and leave is acceptable after a certain age and it is not always clear a who will drop off their kid and who will stay for two hours.
Overall it is a great way to spend a couple of hours.