The front end of this tool is identical to rorys3D's wrench and key for his delightful Little Pit Stop series. The handle should be small enough to fit even little hands, while introducing them to the use of that kind of tool to fasten and loosen bolts (as in this case), or nuts, or screws.

Printed with brim, but without supports, standing straight up, using variable layer height (just to ensure a smooth finish to the domed end of the handle) - using 0.2mm throughout will be perfectly acceptable. I used PLA (but no doubt PETG will do too) with three side walls to improve strength, with 15% infill. Without a brim there may be adhesion challenges, due to the rather small footprint on the print bed, so I highly recommend the brim.
And just to be cute I changed filament colour at the point where the handle started - this, like the variable layer height, is of course merely a cosmetic choice.
Also check out these wheels for your Little pit stop vehicles.
The author remixed this model.
Remodelled the wrench/key into a screwdriver tool.