Hi J.:
My husband is Mexican and I am Canadian. Both my boys, age 4 and 7, are completely bilingual. My husband speaks ONLY Spanish to them. He NEVER speaks a word of English to them, even around other people who don't speak Spanish. I on the onther hand ONLY speak English to them. It helps that I understand Spanish, so when sitting at dinner I am able to understand and participate in the conversation. My husband and I speak English to one another. Interesting enough, both my children spoke Spanish first before English even though I am a stay at home mom and am with them 24-7. My husband puts the boys to bed and reads to them in Spanish. We put Spanish DVD's on for them when possible and we listen to a lot of Spanish music. We do flashcards with them and play games always in Spanish. We especially try to play Mexican cultural games. I also make Mexican foods that encourage interest in the culture and we talk a lot about Mexican history and my husband growing up in Mexico.
If the boys try to speak English to my husband he will tell them that he doesn't understand and makes them answer in Spanish. Sometimes this requires some encouragement and at a young age there is a lot of stubborness, but it has paid off.
My suggestion is put them into the other language as much as possible. Even though we haven't done this, there are Spanish language classes held on the weekend in our community that I know other families have participated in. We ask that our friends and family who speak Spanish ONLY speak and write to our boys in Spanish. We also encourage them to do the same. Research Mom's groups that speak Chinese and get involved, even if you don't speak the language. I've found that it is good for the kids when I make an effort in their language development.
We also have our boys in French Immersion and they are doing exceptionally well because they do have the other langauage. They are able to distinguish sounds that I can't hear and speak with a great French accent.
Good luck and enjoy.
Jenny
As an aside. We also have no family that live close to us, but have managed between my husband and I encourage the language and culture. Our closest family that speaks Spanish is in Vancouver and Mexico. Our closest friends that speak Spanish are in Atlanta.