JM - maybe it's a second girl thing because DD2 is much more forceful and physical than DD1 was. Most of her aggression is directed at DD1 though and she is as sweet as pie and totally empathetic to anyone else! She first bit her sister at 6m old and then quickly moved on to hair pulling, pinching, pushing and hitting.

In her case I think it is the fact that she gets frustrated trying to keep up with her sister and also that DD1 is very bossy verbally so DD2 lashes out by being bossy physically. Maybe some kids just don't limit themselves tho their siblings

In your case too JM she is probably sensing that things will change again with a new baby and that can increase their anxiety - I know DD1 went through a tough phase when I was pregnant.