Protecting Equipment from Children

Actually on second thought.... Fluffy onesie and a Velcro strip on floor and walls to stick them to

Aside from the obvious (grills, unplug components, batteries out of remotes, etc), the best defense is a good offense. Have something else for them to do and occupy their attention. And if you do seem them messing about, just tell them it's broken and doesn't work. They'll quickly lose interest and look for something else to destroy (works wonders with my 8yo nephew and 5yo niece).

How about being firm, starting with your own children. Enough games and enough about distractions...........not even half-measures. 

I can't get angry at the grandkids.  After all, we have a common enemy, their parents

Put the remotes out of reach. 
Install dust cover and speaker grills. 
Unplug everything at the conditioner or power strip. 
Gaff tape the switches and knobs you’re most worried about. 
You can pick that up at Guitar Center or order from Amazon.
It doesn’t leave a noticeable residue and it’s used all day, every day on movie sets. 
Not that that makes a difference, but it speaks to it’s realizability in sensitive situations that are too numerous to detail here.