Guys this one can be tough. There's allot of songs about love, but not too many that describe the love between and mother and her son. These songs are popular with mom and lyrically safe. Try to have mom suggest a song that she want's to dance to.
In To The Mystic - Van Morrison
A Song for Mama - Boyz II Men
You're The Inspiration - Chicago
A Mother's Day - Jim Brickman
Wind Beneath My Wings - Bette Midler
Somewhere Over The Rainbow - Isreal Kamakawiwo'ole