So the idea is to get the speakers out of toddler reach.

Is that to protect the current speakers from the kid, out the other way around.

If it's to protect the speakers, you could be solving a non problem.

The other way around, you likely just need to secure the wiring.

On the third hand, if this is an excuse to install speakers in the walls, just do what is needed. You could build out that stub wall just enough to hold the desired speaker(s).