have the umbrella have a number on it on a board, hand each kid a few raindrops and then call up the number on the umbrella. say "who has 'one' raindrop" they will come up, find and place it on umbrella w matching number.
Frugal April Fun Craft for Kids: DIY Rainy Day Paper Umbrellas: You can’t have rain without umbrellas, right? A great umbrella is the best part of a fun rainstorm. So whip up some mini umbrellas of your own to display.