If you have grills for your speakers, leave them on. It makes the speakers much less interesting, on top of protecting the drivers. As far as protecting the kid goes, the pen idea is nice, but you also have to consider that she might be able to get around it somehow. Kids are resourceful.
I'd either get speakers up on shelves or make the ones you have more stable, ie, add a larger base.
I'd either get speakers up on shelves or make the ones you have more stable, ie, add a larger base.