Bumping this thread to say I was looking for a game to play with my kid and found this game on Steam. Perfect pick! Its just dumb fun, decent little voice acting bits, decent music, and lots of options for free-building both levels and vehicles if you want to go that route. Steam Workshop integration is right there if you aren't feeling clever and just want to download other people's things.
What I was really hoping for was just a "pick a level, pick a smasher, and smash" thing though for kids, and it has plenty of those. In fact, you're spoiled for choice just from the base game, with lasers, catapults, maces, rockets, flippers, gravity balls, giant fans, shockwaves, you name it. Kid and I are having a good time.
Only frustrations I have had are that you need to actually complete the game to unlock everything, and kids are not patient, and that the crane levels can just get pushed into the ocean like all the "push thing into ocean" missions for all I care. Precision crane game this is not.
Instruments Of Destruction is a sandbox, physics-powered demolition sim from one of the tech wizards behind Red Faction Guerilla and it's out in 1.0 now.
www.rockpapershotgun.com