We pray with our children the same prayer every night. You just make one from your heart.
Dear god, thank you for today, thank you for my family and friends. Please help all the sick and poor people and help me to be good. In Jesus name. Amen.
You just pray from your heart your feelings and it will show more than memorizing a generic one. We have our kids memorize the above generic and around 5 years old they start coming up with their own, different ones each day, and from their hearts.