Hi!?!???

Ava is at the stage where she loves to hi to everyone who passes us weather it's adults or children while we are out shopping. I think it's really sweet and endearing. However there are many children whom don't seem to think so. Ava will say hi and they just stare at her as if she has uttered something from a different language or she's from another planet! I understand the whole "don't talk to strangers" but come on kiddos. How can you not say hi to a sweet soon to be 2 year old??  It doesn't seem to be the fault of the parents because I will often hear the parent ask their child, "did you say hello to the little girl?" I know I shouldn't let it bother me but it does. Just one of life's little annoyances I needed to vent about and baffles me each and every time...