How to play:
Use the birthday child's age as the number of the day! If your child is turning four, you will hide four of each item before the party, and later send the guests on a hunt to find them all.
Before the party:
Using the birthday child's age, collect that number of several different items. For example, if your child is turning four years old, collect four balls, four toy cars, four blocks, and four dolls. Hide the items in a separate room or in your yard. Choose fairly obvious hiding spots that are no higher than the children can reach.
At the party:
Explain to the children that the number of the day is [your child's age], and that their job is to find that many of each hidden item. Tell them the first item to look for, such as cars, and send them to search. When they have found all the hidden cars, send them to look for blocks. Keep going until all the hidden toys have been found.