Kitten "Madame" - Boy or Girl?

I am so embarassed to admit that we may have made a mistake on the sex of our new kitten, Madame. I was so sure she was a female, but in my defense, she is a longhaired kitten and the naughty bits are not so easy to view. Recently my husband has said that he thinks she is developing into a boy. I checked again and I see what he means, but she still looks not so boyish, compared to her brother. So, I am taking both kittens to the vet next week for their rabies shots and we will let the vet decide, boy or girl. If a boy, Monet will be the new name.