Would you let your 2 year old play with play dough. I know the recommended age is abot 3. However my LO demands to play with it when his older sister is playing.

With supervision, yes. If not, I wouldn't because I'm afraid that he might put it in mouth. How old is your daughter? If she's old enough to help supervise and tell your son "no", then maybe it's okay to let them play with the play-doh together. Your daughter can practise being a big sister and your son can play with the toy he loves. Win-win! But of course, best if you're in the vicinity just in case something happens :)