We pay the babysitter a flat rate and split it evenly. Whether she works one day or four days we pay her the same rate. Since W and I both have varying work schedules we use the babysitter in varying amounts. Some weeks W uses her a lot, some weeks I do. Some weeks we both do.
And since we have 50/50 custody summer child care is a shared cost and it's legally a shared cost in my state. By statute child support specifically excludes child care expenses. So child care expenses are to be split 50/50 above and beyond child support amounts.
Married 6 together 8 Me:38 W:31 second marriage for both SS12, SD10, S6 Bomb: 9/8/11 (day before our 5 yr ann) W moved out: 2/18/12 D final: 11/12/12 Share S 50/50. Spend as much time as I can with SS & SD