You want too much and your expectations aren't aligned with reality. You want women who will treat your kids as if they were their own & then not get upset when you break up with them? Ridiculous.
If you want to keep it light and casual, don't introduce these gals to something as important as your kids.
If your kids are young, you shouldn't even be introducing them to your flings until you are reasonably certain they are somewhat permanent. Kids can't control their attachment to people, especially if they are looking for a substitute mom. Don't you claim to be the responsible parent?
Second thoughts can generally be amended with judicious action; injudicious actions can seldom be recovered with second thoughts.
--Cyteen by C.J.Cherryh