I feel you... I am somewhat in the same place, great company, flexible schedule, but I know I am worth more and could find something more challenging and with higher pay than what I am in now.
I have been doing lots of soul searching and here is my 2 cents... I think the issue is that there are so many uncertainties with a new job - you could also be mind numbingly bored but now you wont have tenure. on the other hand, you could find an amazing job that is family oriented and allows the best of both worlds. you just don't know until you start looking, but those risks will always be there.
anyway, I would say you should look around, but be very picky with where you move. only look at places you know have a good track record (maybe you know someone that works there?). even though you don't like your job, at least you have one and yes sticking with it means you have time for your family, so take advantage while you are there and if something perfect comes along, take it!
btw, that is somewhat what I have been doing. I have 2 interviews next week, both at places where I know people and I know they have a strong track record. I also have a $ in mind that will make it worthwhile to take the risk. if I don't make that $ I wont move... at least for the time being... we shall see!