This is a really common problem for a lot of moms I know! Plain and simple, tell the child to go home. A 9 and 5 year old have little in common and it sounds like this child's visits are more unpleasant than a fun playtime. If your son wants to play with him, offer to meet outside to play for a while and when things start turning sour you can just say "Thanks for playing Jimmy, we have to go in now so you should go home now." If he is in your house and you want him to leave, say so. You don't need to offer an explanation or an apology, just say, "Jimmy, you have to go home now!" If you know his mom or his phone number, call when your son wants to play and offer to meet outside or tell his mother a specific time frame and stick to it. You may also want to add that in the future, he should call first and save himself the trip in case you are busy. A polite guest would always call first and they may need to be gently reminded of this detail. If you'd rather he not come over or come inside, just turn him away at the door. You can add that it's not a good time for your kids to play, or that you have other plans right now if you feel the need to give some explanation. If you turn him away repeatedly, he will find something else to do and will stop coming around.