When should co-bathing stop? Is there a gender difference as in only daddy bathes boy and mummy bathes girl?

For me,once my child starts talking in sentences and able to give description about things (in this matter, about our bodies) then i stop co-bathing. I don't mind doing it with them when they were babies coz bath times can also be playtime. :) And my husband bathes our kids (girls n boys) more than i do. We both let them bathe themselves around 6 y/o.