When my children were in the pram it wasn't unusual for complete strangers, always older people, to stick their finger in their mouth for them to suck, poke them in the belly to make them laugh (it usually made them cry) and say things like 'oooh, I could eat her up/I could munch him/I could take her home'.
They were being friendly. Usually they put a silver sixpence in their fist, occasionally a shilling - to bring them luck.
Many old people miss their babies, are sometimes lonely and enjoy a bit of human interaction. It is true some are perverts but I can't see any sexual harassment in this incident.
What good would a lawsuit do you? It's a very stressful thing.