Why the formality in prayer?

Last night as I was trying to get Aria to say prayers and go to sleep, she began to ask me questions about prayers.  "Why do we say, "In the name of Jesus Christ, Amen?" she asked. I tried to explain it to her, although probably not clearly for a 4 year old to comprehend.  Aria responded by saying, "Why can't we just say, "Goodbye." "  I told her that it was probably fine to also say "Good-bye," and maybe a "I'll talk to you tomorrow" as well.  She said that she liked that better.  Then she looked thoughtful again and asked, "Why do we say, "Dear Heavenly Father"?"  I told her it was because we are trying to be respectful and polite, but she could also include a "hello, are you listening?" if she wanted to.  For our prayer, I tried using those more informal words, and it was interesting how it really made me feel more like I was talking to a real, living Being that was listening to me.  After I finished the prayer, Aria smiled and said, "Hopefully Heavenly Father is okay with that."  I asked her if she thought He was okay with it.  She said she didn't know.  I said that I thought He was "okay with it."