Pray the same prayers every night before bed with your child.
Pray in the car on the way to sporting events, or wherever. Pray for safe arrival and the kids can learn their prayers at the same time. From little on, it is the repetition that helps them memorize and if you have younger children they will easily learn their prayers before you know it!
Prayer on the way to Mass, it also helps prepare your children to enter into the gift of the Holy Sacrifice of the Mass.