I wouldn't suggest seeing a dr, but I don't see the harm in his snotty nose coming up in conversation. DS was the child with the awful sounding cough and drippy nose all season (asthma related more than anything) and I wouldn't have minded it coming up. Just commiserate with her about how hard colds can be to shake and how kids seem to have them one on top of the other sometimes. The conversation can flow then and just see where it goes. He might just have allergies or something. Ds's asthma and eczema both seemed to flare up in the cold season.

If its green coloured or anything the carers should be saying something themselves to the mother. But there's not much you can do for the clear drippy noses :/