I really don't want to spark a "you aren't working, you shouldn't charge" debate here. I know most c/m's charge for bank holidays, and I presented an invoice for the month with those dates on as normal rate.
The mum questioned it this morning, and perhaps I should have had a better answer, but I just said it's normal procedure amongst most c/ms. In fact I remember being surprised when my old c/m charged me.
I still feel bad though.