Hun, while at the same time as saying please don't worry too much, they do all reach things in their own time, if you are concerned, then do seek some advice. As her mum your instincts are probably finely attuned to her wellbeing and you are likely to notice things others may not. Don't be concerned by comparisons (my goodness, those never stop!), but if for no other reason than to put your mind at ease, go and see a paedeatrician and get some professional advice if you have concerns.