Well, if you want to 'control' moods (like I often do), you already have a very powerful tool, that doesn't even require a 3rd-party program: Savescumming. Some players may regard moods as being handed down directly from Armok, and so attempting to direct or manipulate them would be little short of blasphemy . . . other players may feel that milking the situation for its maximum possible benefit is precisely what a dwarf should do, and accordingly build forts full of Legendary Farmer/Dabbling Weaponsmiths. I think that savescumming, while admittedly completely unrealistic (Kadol the Fish Cleaner has been possessed! Oh no, wait, that didn't happen. Bembul the Mason has been struck by a fey mood!), do make for a nice "middle ground" on the roleplaying/powergaming continuum, because it forces you to choose between the utility of dropping your child's mood for the chance of having it strike your Armorer, and the ease of not having to replay those last 4 months all over again.
I agree that moods shouldn't happen quite so often . . . I think I'd cap them at a maximum of 1 per year, and/or depend on a dwarf already being emotionally unstable. It would also be worth considering to have the moods prompted (or at least influenced) by specific gods, or even demons. But as for outright preventing children from having moods, I don't think I agree with that. If anything, kids are less stable than adults, and should be proportionally susceptible. If/when "child" labor is reworked, so that individual jobs have different (and therefore generally lower) minimum ages, that should be enough to mitigate the "Oh great, the 9-year-old's gone secretive. Get ready for another native platinum scepter" problem.