Yes, you search upstairs

You are confident he’s not downstairs which means he has to be up.

Once upstairs you take a peek around to see what you’re dealing with. From here you can see two rooms with open doors.

One is a game room looking area and the other is a bathroom. Then there are four closed doors.

One is obviously the master bedroom. The one nearest to that one is covered with princess stickers so you suspect it’s Julia’s. The other two are just plain doors which means one is probably Tommy’s room and one is Cameron’s.