No, children do not have to board - there's the option of the parents living apart and commuting when possible and there's the local state option.
However, as someone earlier in the thread pointed out, getting your child into a decent school can be incredibly difficult when you're moving mid-term or when you only get your address 4-6 weeks in advance. What about a posting that falls slap bang a month before exams (although delays in moving house are sometimes allowed in such cases)? For us, especially, there is the difficulty of ensuring our children get a Catholic education - for which we are prepared to pay privately as a day option if we can't get it through the state.
We had seven houses in as many years as my husband was trickle posted from job to job and the thought of dragging a child through that was not attractive - however, neither is the option of putting them in boarding school. I think that Forces families are often caught between a rock and a hard place when it comes to family life - there is no ideal situation.
I may be wrong (and I'm happy to be corrected) but aren't RAF posting a little less infrequent? The couple of people we know in the RAF seem to have a little more stability than our Army colleagues. Perhaps that depends on the job/specialism, though.
When I said that civvies don't understand I was not "bleating" - I was merely pointing out that having your whole life, career, family education placed at the whim of the MoD can be a difficult thing to grasp unless you've gone through it. Much the same way that while one may sympathise with another's situation (whatever that situation may be - divorce, bereavement etc) true understanding only comes if you've been through it yourself. Does that make sense?