We started the ducklings praying before they could speak, as soon as they could sit up during family Bible reading. We'd hold their hands and help them tap the appropriate family member, saying, "Thank you for Papa, Mama, D# and me! Amen!" Pretty soon they learned to do the tapping themselves, and as their language grew they supplied their own Amens, names of family members, and eventually branched out into thankfulness for whatever struck their fancy. (Especially doggies. And trains.)
So far, though, neither of them has realized that there is a way to pray besides saying "Thank you." Whatever petition comes to mine, it is couched in terms of gratitude. "Thank you for the pastor going to Othopipia." "Thank you for Mama's cold." (ahem!) But then, I suppose there's no better way to pray than in gratitude for all things and in confident faith in the goodness of God's answers.
And they have many, many things for which they are thankful. Houses. Toys. Family. Friends. Wheeled vehicles of all kinds. Animals of every description.
One evening D1 provided a short but earnest prayer, "Dear Heavenly Father, Thank you for all the laughing." Amen.