Black Hole Girls- I only mentioned this game for one reason. Namely, in BHG, you play as a 12-year-old girl with a pet alien supermonster. The thing is, you roll different sized dice based off of who has more control in the relationship, the girl or the monster.

There is a dice distribution that looks like this:
1d4-1d6-1d8-1d10

When you start, you pick for one side to use 1d6s and the other to use 1d8s. Through-out the game, you adjust the dice sizes along the scale; if you increase one side by one step, then the other drops by a step, and vice versa.

Where am I going with this? You can have a similar mechanical back-and-forth between the teddy bears and the monsters; it would make for a good "oh crap" moment for the players, at least, when the dice they are using drop from d8s to d6s, or worse, when the child they are guarding starts having a nightmare. Or, maybe tie it to the time of night, so that your strategy has to shift through-out the night...
If you're tying it to the time of night, I suggest having the scale start out heavily in the bear's favor, then slowly degrade as the knight wears on, as it's always darkest before the dawn... if Dawn breaks before the child wakes up, the bears should be empowered again I think.

It also allows you to apply time-based pressure, like trying to destroy or weaken an insanely-powerful nightmare before you become too weak to fight it.