Each one of us has a guardian angel who protects us from harm, both physical and spiritual. In this prayer, traditionally one of the first that young children learn, we ask our guardian angel to watch over us.
The Guardian Angel PrayerAngel of God, my guardian dear, to whom His love entrusts me here, ever this day [night] be at my side to light and guard, to rule and guide. Amen.
You can find other prayers for children in the Top Ten Prayers Every Catholic Child Should Know.