My son is 6 and I still sing to him.
What ages are your children and what songs do you sing to them?
my daughter is 6 and I sing with her during the day ( i play piano & we sing ) and I sing to her at night while rocking in the rocking-chair or lying in bed with her. I sing her lullaby songs or just hum a nice song. 
I think 12 would be about the limit, they’ll just get annoyed and weirded out when you sing TO them at that age…