Speaking Chinese to My Boys

My wife and I came from Taiwan when we were very young about 7 years old.  As such, we do not speak Chinese to each other, or we would sound like a couple of 7 years olds talking to each other.  Even though our conversation typically is not all that deep, English is still our means of communications.  We debated about speaking to our 4 boys English only, since Chinese is our heritage and we felt very guilty that we weren't doing more to pass on that heritage.  With our 4th and last child we decided to give it a go and speaking Mandarin to him at home.  To our surprise he has grasped it beautifully, which made both my wife and I feel even more guilty that we did not make the effort with the other boys.  Well all of that changed for me when my wife came home excited that she had found a Mandarin tutor for our 3 other boys.  At a mere $70/hour, which was noted as very reasonable, the tutor would come to your house and speak with one child at a time in Mandarin.  The rate is much higher if we wanted all three to participate simultaneously.  $70/hour!  That was enough motivation for me to start speaking Mandarin to my boys at home.  My wife is not convinced that it will be affective, so I told her that after one week, if the experiment was ineffective/non-productive, then we can reconsider the tutor.  Last night I tried to speak only Mandarin to all my boys, with a lot of empty stares by at me "huh?"  I'm not giving up that easily.  This morning the boys said "jouw", which means "good morning" to me and I am once again encouraged that little by little they will pickup the Mandarin.  Even if I have to pay them $70/hr to listen to me, it would be worth it.