Try not to be upset - kids say whatever pops into their heads and they are so likely to say something that hurts us but that they didn't mean in that way at all.
At work I have 2 staff called Emma. One is 5ft 4 and the other 5ft 1. Both about 8 stone max. The children call the 5ft 4 one 'Big Emma' and the otehr one little Emma, even though, apart from the small height difference there is nothing to choose between them.
My grandaughter calls my Mum ' Big, big big Nan Nan' - my mum is about 4ft 10 and a massive 7stone! I am over twice her size. Work that one out.
Don't worry, we all think you are lovely! Because you are!
Love