Some obvious sugestions:
If childhood were music it would be
Mozart: Ein Madchen oder Weibchen- aria(Papageno) from The Magic Flute
(and there is much more enchanting innocent music from this opera).
Brahms: Berceuse
Liszt: Consolation #2
Schumann: Traumerei from Kinderszenen
Chopin: Prelude op.28,#6 (if I'm not wrong this is the simplest, loveliest
one)
Beethoven: Alla Danza Tedesca from one of the last string quartets
Bach: Prelude #1 in C major from the Well-Tempered (book I)
best regards
Marcelo