Hi rathernotsay,
I am in a similar position, although I am further down the track. Sorry to be negative, but I think that you are up against more than you realize.
You sound like a principled person. (I consider myself the same.) The first thing to realize is that they don't play fair. I did not get that at first, because I did not know much about JWism and I didn't expect a Christian religion to be so dishonest. They think that your kids' lives depend on them being indoctrinated, and that entitles them to say one thing and do another behind your back.
They're so young and I imagine that they will make their own minds up eventually...
That is probably the norm in most Christian religions. However this religion makes it really tough to leave. They use psychological pressure such as cognitive dissonance. It is particularly tough on kids because they tend to believe anything told to them by adults. A lot of kids do eventually work it out, but at best it is painful.
As far as solutions go, I don't have any at the moment. I am still battling. Wife and kids go to meetings. I can't stop that. None are baptized, or express much enthusiasm, but will be very defensive if I mention anything negative about Watchtower. At this stage I don't know which way my kids will go. I have managed to get a bit of TTATT into my wife, and she doesn't seem to have the confidence in it that she used to.
It is probably a good idea to keep their minds enquiring, whether about space, dinosaurs, or whatever. One think I found is that the school teacher is your invisible ally. Your kids have probably already got the message that you can not be trusted on matters concerning religion, but I have noticed that they still trust anything the school teacher says about science, evolution, etc. I have tried to give them as much info on physics etc, and when they hear the same thing from the teacher, it is confirmed as fact.
This is Machiallelian, but another thing I have done is physically move the family to where contact with JW relatives and JW's generally is difficult. As a result, my kids don't have any JW friends, and generally only see other JW's at meetings. I think that might help, in the future.
There is a lot more I could say. Anyway, good luck with it all.