We have Sky here which also has the English/Spanish option for most channels so they watch 99% of TV in English - my 6 year old daughter even complains if the TV is in Spanish which I guess is a good start but kids will be kids and they just won't speak it! A couple of years ago we moved to Canada for about 18 months and my daughter went to a preschool and started speaking some English so it's obviously related to speaking the language of your friends in order to fit in whereas she knows mummy understands Spanish so why make an effort!!! In fact she makes more effort with her "English" teacher at school than with me! Thanks for all your advice.
You are right , it is so tough continuing speaking a language when it is not spoken around you. This is how I lost the German I knew and this is how my grandmother whose first language was Basque lost the ability to speak it after many years of not speaking it. She continud understanding it but would answer back in French.
My Zapotec friends who live in Ajijic have children who understand Zapotec but do not speak it, they keep saying that after a summer in Oaxaca they will speak it but the 11 year old will not learn how to speak it correctly anymore unless they sit down and teach it to him.
May be some vacations around an area in Mexico where many people speak English will help.
I met a little French girl in a store here in AJijic who was blown away when she heard me speak French to her. She asked me where I had learned French not realizing that they were other people in the world who spoke French other than her family.
When all the friends speak Spanish the kids want to fit in and speak Spanish so it is a tough problem if they do not speak English before they go to school.