Make sure you go over the rules for playdates with your child before the visit. Discuss things like sharing, letting the guest choose first, and compromising.
Kids forget from time to time.
I find that if kids all play something together for the first half hour, the playdate gets off to a great start. I build some downtime into most playdates by offering to read a story. Even the older kids, who can read by themselves, love to curl up on the sofa and hear a chapter from a favorite book. With a break like this in the middle, they seem to cope better with the visit. After a day in school, a three-hour playdate is too long.