What Would You Do If You Caught Your Four Year Old Beating Up Their Younger Sis?

Time out is all you can do--siblings fight. That's what they do. Time outs, taking away toys, privileges, whatever. Oftentimes, you'll find it's easiest and best to let the kids work it out for themselves. If your 22 month old wasn't crying and was fighting back, then she should be given a time out, too. She's plenty old enough.