Why do we need prayer?

During a conversation with a group of 9-12-year-old children about intercessions and petition, a catechist asked, "Why, if God loves us as you have said, and knows us and knows what we need AND how to give it to us--why then do we need to pray for ourselves and one another?" (The catechist was very honestly asking this question of the students, as it had puzzled her for years.)
Ursula, age 10, said, "If I give you the gift of my pencil--(and here she held out her pencil to the catechist)--the gift is not complete until you take it. That's what prayer is: taking the gift God is holding out to you."