Summary

IMPORTANT - print and assemble according to instructions if small children will be playing with it.

I was inspired by: https://www.thingiverse.com/thing:2121444
Unfortunately, the orientation of the layer lines in the original design means the barrier supports can be fragile. I address that in this design by printing them separately.

Printing

The two braces should be printed on their sides. Ensure they're solid by setting perimeter layers to an arbitrary high value (rather than setting infill to 100%). The braces will be strongest this way.

The base and barrier are printed as you like.

Assembly

Before painting and gluing, insert the braces into the base, using a hard surface to tap them in if you need to, and then wiggle them back out again. This is so you know the tolerances are good before you paint parts or make any mistakes with glue when the parts don't fit properly.

Paint the pieces if you want, but don't paint over the parts that'll be glued together.

Glue it up. The only risk is that you don't use enough glue - the toy needs to be strong enough that a toddler won't break it to pieces on day 1.

Update 8/9/2020: I can confirm that standing on the part barefoot is not recommended. The part will survive, your foot will suffer greatly. Honestly, if that's a risk don't even print this.