Candy Toss
In place of having kids jump up for the bouquet toss, have someone toss an assortment of candies at another end of the room, or outside. Or, instead of throwing candy, set up an area where kids can break open a piñata full of candy. Be sure there is adult supervision when this activity is taking place.
Balloon Games
Since balloons tend to be popular at weddings, blow up a few balloons to use in children's games or competitions. If the reception is held in a large enough hall or outdoors, have a balloon race. Have each kid line up at a starting point while clasping a balloon between his legs. Choose a designated finish line. Stand with your arms outstretched, and the first child to clap your hand wins. The children must race with the balloons between their legs at all times. They cannot use their hands to hold the balloons in place. If the balloon should drop from the leg while racing, that child is out of the game. Have a candy prize ready.
Movies
If your wedding party should continue through the evening, host a movie night in another room. Gather all of the children in the room with popcorn and a G-rated film (usually animated flicks are best). This will keep them from feeling too bored after a long day and night.
Dancing
At most weddings you will find some sort of entertainment, whether a DJ or live band. Keep kids entertained by encouraging them to the dance floor. Have the DJ play some fun children's songs such as "The Chicken Dance," "Macarena," "Limbo" and the "Hokey Pokey." Adults can even get in on the fun, too.