seperation child care legalish help

Me and my wife separated(nothing legal yet). We agreed to share our child equally by switching every week. She wants me to pay for half of her daycare expense. My mother is currently watching her when I have her so I have no childcare expense. Should I pay for half of her daycare expense or should she pays for daycare when she is with her and I take care of the daycare when she is with me by having my mother do it?

I would appreciate some references if you know of any or if any of you have been in a similar situation to share advice.

Thanks