Ann - I missed this thread but want you to know that I think this is wonderful! I'm jealous!!! It's my dream to move to another country for a few years with my family. My sister lived in London for 2 years (3 yrs ago) - her husband also had a job transfer there. They lived in Fulham which is a GREAT area! Could you look into Fulham? The soccer stadium was just a few blocks away and on game days, the streets turned into a parade and so lively. My sister was a SAHM with her twin boys who were only 1.5 then. While she was there, she ended up getting pregnant and having her daughter in London. I'm sure she can help you with some ideas - PM me if you want her email address. She found several mom's groups and ended up enrolling the boys in a little school a few hours a week which was soooo cute - they wore uniforms. When they came home, all of the teachers in the states say that they are so well mannered and ahead of their classmates here.
I know it's so hard to leave your friends and life here, but I think this will be such a great opportunity for you and Gwen and Paul. You can take weekend trips to Paris, Malaga and other fabulous places!! When you get back, all of your friends will still be there and welcome you right back and you will be more full of life for having this great adventure.
Good luck getting all of the arrangements in place and I'm soooo happy for you!!!!
ps - I also have good friends who have a 1.5 yr old boy that live in London and can help you with questions. I'll send you their info - they are great! The mom is English and the dad is one of my husband's best friends from CA.