Guessing games.
This can be adapted for all ages depending on what you fill your “guessing jar” with. Small candies or goldfish crackers can be used for older kids and larger items like apples or oranges can be placed in a container for the little ones.
Give everyone a piece of paper to write their guess on and at the end of the carnival, all the kids can help count out the items in each jar with a prize for whoever has the closest guess.
Mom and Dad can also gather several items from the dollar store to place in a large basket. Kids can be blindfolded and try to guess the objects they pick up. Try to find objects with interesting shapes like plastic animal toys to make it a little more difficult.