Ecto is a very fast-paced shooter playable in solo or online co-op up to 8 players, where you bunny hop around blasting robots with flower guns.
It sounds, and looks, rather bizarre. I'll be honest - I read the Steam page, watched the trailer and I still don't entirely know what the heck is going on here. Wild. From the Steam page: "Ecto is a highly-randomized nature world, featuring smooth, addictive movement. Jump around on colorful, nature-inspired floating islands with your friends or solo. Pick up trinkets, buy and upgrade stick guns, hang out with frogs and fight robots in the underworld."
Check out the trailer:

Direct Link
In the latest announcement the developer revealed the new Native Linux version with a note:
LINUX SUPPORT!!! This was actually so painful to get working but I had to do it for the love of the game. If I see the word "libsteam_api.so" or "SteamAPI_Init" one more time I'm going to lose it.
The update also has a bunch of other gameplay tweaks.
Ecto is currently in Early Access and the developer considers it "pre-alpha" level. Eventually, once it's finished, they do plan to attach a price to it. But for now, it's free while they build it up.
Ecto is a highly-randomized nature world, featuring smooth, addictive movement. Jump around on colorful, nature-inspired floating islands with your friends or solo. Pick up trinkets, buy and upgrade stick guns, hang out with frogs and fight robots in the underworld.
That sounds like exactly the little one's cup of tea.