Thanks for the answers.
This was something that just came up since my SO is up for a job that will take us 6 hours away. No one saw this coming so they didn't talk about that or have anything written in the paper work about it.
The kids would be with us for the entire time, probably the entire summer and unless the mom wants to drive 6 hours to get them she won't see them during the time they are with us and that's why I asked. He pays 3000 bucks now for child support and that would double to 6000 if he gets this job so it seems like a lot to hand over to someone to care for the kids when she won't have them but if that's the norm he won't protest.