What about the sock monkeys? How about placing a hellium balloon in one of the monkey's hand (arm up)? and nestle the pic frame in his lap. Put a party hat on him and a party blower by his foot. Or peel a banana and place the peel upside down on his head.
Or find more realistic monkeys, and make little cages to place them in., (perhaps out of a double wide cereal box- cut the 'bars' with an exacto knife) and then spray paint them grey. put tan raffia in the bottom of the cage as "straw". Place a note or a tent card nearby, "don't feed the animals", throw some peanuts around the cage. Perhaps some of the notes could read " This place is a zoo!" Cut out a male's shape from heavy card stock- dressed like an animal trainer in khakies and a safari hat. Glue your sons facial photo where the face should be! Put a stand on the bottom (like paper dolls used to have). Place it next to the cage. Get a piece of jewelry chain -attach/hot glue it to the hand of the trainer, and then to a collar around the monkey's neck.
Favors: a barrell full of monkeys toy, animal crackers, peanuts.