¡Al ataque kung-fu kids!

My parents rented this for me in the 80's, I dubbed a copy and still watch it now and then. This movie is something like an earlier 3 Ninjas, it's about a trio of boys who learn martial arts from their grandparents. Grandma wants them to go to school while Grandpa wants to keep training them, so they have a duel. You've seen the scene in other movies where two combatants fight on top of tall wooden posts- here, they fight on top of dozens of soda cans stacked in the yard. Grandma wins with a dirty trick, so the boys get sent out in the world- hilarity and numerous painful groin shots ensue.

This movie is long out of print, you'll have to find it on VHS if you want to see it. Your boys will probably love it, we all wanted to be ninjas at some point.