I have a few ideas- "Godspeed" by Dixie Chicks, "Wind Beneath my Wings"- Bette Midler, and the one that I have been singing to my son since he was born that brings me to tears is "From This Moment" Shania Twain/ Brian White. Also for your daughter- because I also have both a son and daughter- "In My Daughters Eyes" by Martina McBride would be perfect or "Because You Loved Me" by Celine Dion.