SOL, wouldn't worry if I were you.
Talked to my mum earlier, my stepsister (her dh's daughter) had a baby in mid-March, and apparently H is worrying that her son's not sitting up unaided etc. We agreed that she shouldn't mention D's 2 teeth to H or to my mum's dh, as he says some rather undiplomatic things to his own daughter! The point is anyway, they all do different things at different stages, however much we'd like to believe our own little darling is smarter than the average bear cub, they'll probably all get to around the same place in the end in different ways.
Just had a lovely piece of news tonight, my little sister has been offered the job she really really wanted, a training contract as a solicitor. The firm she most wanted to work for as well.