That is a huge difference I have noticed between girls and boys, and completely normal. About a year ago I read the book "Why Gender Matters" and it is the most amazing book I have ever read! It explains so much of those differences you will notice, and why, and is even a huge help when it comes to adult relationships... just in understanding why they do the things they do! I could read that book a million times and still love it! I have ADD, and in the last 10 years there have been very few books that I can get myself to sit down and read and actually finish... I can't concentrate well enough... I had this one done in 2 days because I couldn't put it down. No other book has had me like that in over 10 years... I don't know if I have even finished another book in the last 10 years... I think it would be a huge help to you having twins to understand the differences that are normal and why they are so different. Good luck!