Child Damage Mitigation

I used 2 of those plastic gates to close off the living room where my system was, also used those for the stairs. Get them put up asap that way the kid is used to them and not inclined to mess with them. Worked on my son, and my dogs. With the dogs after they got to be about a year old I could take down the gates and they just wouldn’t go in the room. 

The famous Bose 901s were either set on a "tulip" stand
or suspended by chains from the ceiling.
I think you can see which method would work best
for your situation.
Enjoy you new gift. 
Stereo gear won't be a priority for next 18 years or so.

In a little different approach, I feel the kids should be allowed to touch all the things with some directions, if possible. However, and that is why bottom-heavy large-base speakers were my recommendation, it may be unavoidable that a child bumps into something while growing up so that particular thing may need to be set up safely.

+1 pictaker5 
perfect solutions indeed 

For those of you suggesting stand-mounts - be careful there as well. My 3  year old son was able to poke a hole in the tweeter of a nice pair of Mission Speakers with a pencil. How or why I will never know . A replacement tweeter was in the cards and an easy fix. the same son enjoys those same towers now in his house 27 years later powered by Rotel . Built like a tank. 

Now the other son found a way to use a small rock to scratch the paint on a near concours 74 Alfa GTV that was in the garage . It wasn't as easy a fix and I surely  didn't forgive him for quite some time. AND no he doesn't have the car in HIS garage :)  !

Good Luck , nothing more rewarding than raising kids. 

Speakers you have heard advice on. If your amp or preamp allows you to limit the volume, you may want to keep that in mind. My boys are teens and I still limit the max volume.