Having just had my daughter start secondary I can see that it’s a bit harder to get to know the kid and parents beforehand. Primary school is so much easier for that as you’re there to pick up and drop off your child, but now she makes her own way to secondary on the bus, so no hanging around in the school play ground for us parents!
I can only say that for me, I would engineer it so that the child could come back for dinner and then you can drop the child home before any sleepover, so you can at least meet them. If you talk to your child too about school and their friends you should get a general feel for that child too and if there are school events that parents attend, ask to meet them/their parents.