Quote bubbles in frames, use a dry erase marker to write funny things your kids say. When you are ready to switch the quotes, have the child take a picture with their quote and make a photo book of quotes.
We've heard of custom framing sheet music from a special song before, but how about framing the sheet music from a favorite lullaby or nursery rhyme for baby's room?!? Consider using matboard to coordinate with the nursery's color scheme an d create a lovely grouping to hang over the crib or changing table, or even in a corner with the rocking chair! This piece could grow up with baby and become such a wonderful family heirloom in the future!