No such thing as adult friendly let alone child....simple to play with - depends on the size of print, consider one from Monoprice if you don't want to assemble everything.
The kit style does provide a very interesting education on what makes the printer tick.
Design software will be fusion 360 (student / tinker /under 100k business) is free.
Cura as a slicer
or was that http://slic3r.org/
The best "low end" kit that busts your budget prsua MK I3 IIs
The best assembled "low end" setup: https://www.lulzbot.com/about-lulzbot-3d-printers
what you should get if going "pro" MakerBot Replicator+
The Tevo style printers are a good kit; lots of mods are required to make it work better and become safe(r).
The first thing you end up doing with the lower end kits is to print parts out to make the kit less low end. You do know that some of the local libraries do have 3d printers that can be used? I know Colorado Springs provides access with support I think from Maker space. You do need to take the safety class, and they might require adult supervision.
To kick the tires to see if it is worth your time? https://www.monoprice.com/product?p_id=21711
The big disadvantage to the above printer is what materials you can print....
https://www.monoprice.com/product?p_id=13860 does provide better options for printing materials and the size of the object.
Join the facebook groups for 3d printers that you are interested. I does provide some good info that might direct you which way to go.