How do mums deal with strangers touching childrens faces in public

Im interested to see how other mums deal with strangers touching your childrens faces/heads in public. I know this is done in kindness but every time we r out strangers touch my kids faces or heads or even hug them and say how cute they are. I know people mean well but i dont want my kids to think its acceptable, because one day one stranger might not be doing this in kindness and my children will not know how to differentiate between good or bad strangers. One time my toddler was throwing a tantrum in a shoppping centre and crying and one woman picked him up and asked him to stop crying. i was totally gobsmacked. Has this happened to to other mums here and how do you deal with it?