TheLocalPlumber
Mr. Gilmer, Although you have properly figured out that it is when the girls take a bath, my guess would be the problem leak is in the waste piping,not the water service line, probably the overflow from the tub is loose and needs either replacing or tightening. It is an easy test to make for a Licensed Plumber.
Good Luck,
Bill
The Local Plumber
Tustin, California http://www.TheLocalPlumber.com
