Every night I lay Kaitlyn on her side with a bigger pillow under the top leg. She likes sleeping on her belly, but wants to roll there herself. A couple times I've put on her belly and she cries rolling back to her back.
I take one Always thin pantiliner and put it on the inside of her cast where it rubs on her skin.
I lay her across my legs and pull the cast up causing a nice gab.
I slide the pad in under her cast; with the sticky side towards the cast of course.
It can be tricky at times when she's wiggling, but it's possible. I leave a little bit to overlap the top of the cast. It doesn't cross over to the front much; mostly just the top of the cast.
After I did this the first time Kaitlyn's cast rash cleared right up. Once in a while the pads must be pulled out and replaced. Sometimes she pees up her cast soaking the pads and other times, like last night, the pads are falling apart and need to be replaced. Because of rubs she wears three pads, one under each arm and one in the middle.
Here's a couple videos I took last week after changing Kaitlyn's pads.