I sorry guy.
Thats really to bad. You could try using low tack painters tap and lay it across the cap. Then you can try to 'pop' it back out.
If that does not work you could move your way up to regular painters tape and then possibly masking tape. If that still does not work you could try the clear packing tape.
I am not sure what the caps are made of on your speaker. If it is some form of plastic it will be harder to pull back out, but it will take more force and a sticky tape to do it.
If cap is paper it should come back out pretty easily but a stronger tape could take some of the cone with it.
I would experiment of similar surfaces before you try anything.
Hope you have good luck fixing it.
Let is know how it turns out.
Cheers,
Nick,
P.S. You could also let your nephew and any other small children know that any poking will result in there finger be severed with a butter knife and then feed to the birds. :) Just kidding. But you might want to look into getting some sort of grill for them. Then when kids come over you can have a little more peace of mine.
I am always worried about some one knocking my speaker over of its stand. My wife says if I am that concerned I should put them in the corner.
She just doesn't understand. :(