That is why you should leave the teaching to a teacher :)
Well, I am not so convinced the effectiveness of a teacher/language course in my situation. It's just that this is way different than for a motivated adult like you. Also, it's hard to find a teacher for 10 and 12 years olds. There aren't many Polish courses intended for children (I actually think there are none in where I live).The only other option would be a private tutor, and most of the ones I can find here are as good in teaching as I would be (or simply put, Polish nationals w/o much teaching experience just looking for a job), or they are insanely expensive here.
Do you have kids? If you do, you'd know that children during class will just zone out and the progress would be minimal. Now being a father I know I can get some of their attention for about 1-hour long lesson. I think with a good course to follow I could do same, or possibly even better than a pro. I learned few languages myself, so I do have some clue what works and what does not. Nevertheless, in the end, the time will tell if this would (or wouldn't) work :)