They refuse to use the bathroom, even when it's really obvious they need to. Second-grader keeps peeing their pants at school, kindergartner keeps peeing on the floor at home.
My DD had the same issue about holding it. She is much better now, but she just did not want to stop what she was doing to go pee. She had so many accidents, even till second grade. One time she pooped in her pants during summer camp when she was in second grade because she didn't want to use the bathroom at the camp (it was a porta potty and gross, per her).
It got so bad that she ended up having a blockage (poop backed up). It got so bad, she ended up in the ER.
The pain was so bad that she doesn't ever want to relive that pain again, so she now knows to drink a lot and go pee regularly.
It was super frustrating. DD is my youngest, and the older is super easy, but if I had two difficult little kids, I think I would feel like you do.
Is there a routine for your kids? I find kids at that age do much better with strict routines.
I hope things get better for you.