Ryn,
In relation to the comparisons between little cousins.........my best advice is say nothing and play it down.
I have 3 SILS, all with children/babies the same age as mine, and it is a potential mine-field I reckon.........Granny and grandparents can be a shocker too, without meaning to be.
Bear this in mind.......if a baby/child excels at something or reaches a milestone really early, chances are they will be later to achieve in other areas.........for example, I got frantic that Olivia wasn't walking, as her little cousin (who is the exact same age) was. By the time Olivia was 20 months she FINALLY walked. Her cousin had been walking for practically a year by then! In between times though, Olivia was having full on conversations, where her little cousin was still on one word vocab. See what I mean?
Luckily my SIL and I are both relaxed and not competitive, and are v.close friends, but I am still very cautious just the same..........
