I'm chiming in to say DD, 5.5 has done the following since baby brother was born:
talk about wanting a penis
insist she is a boy
put all kinds of objects in her pants to pretend she has a penis
pee "like a boy" standing up at the toilet (and actually doing an OK job
obsessively try to touch little bothers penis
comment on little brothers penis (look mommy, it's wiggly, I really like it)
ask if everyone she sees has a penis
I think she is pretty normal. Especially for a little girl with a new baby brother.
I would not even consider that she is transgendered at this point. No offense to previous posters but that leap seems like saying someone might have a brain tumor because they have a headache. I would need to see a few more "symptoms" before going beyond normal gender curiosity as an explanation.