My 6-year-old daughter keeps getting wedgies

Exactly as the post title says, my 6-year-old gets wedgies CONSTANTLY. Any time she moves, she's picking a wedgie out. To be more specific, her underwear keeps getting stuck mostly in her bottom, but occasionally up front too. It's embarassing and uncomfortable for her.

I've tried different brands of underwear with different thicknesses and thicknesses. I've also tried different sizes, but maybe they are all too small. I hate to keep buying more and more hoping something works. Has anyone else had this challenge? What solved it?