TPU print to cover the ends of the handlebars.
It has a grippy hex pattern surface.

The ends are having bigger brim to have the handlebar more save.
If the kid fells on the handlebar it is less dangerous that way.

Just print it in standard settings. I used black TPU with 64D shore hardness.

size of the grips:
16 mm inner diameter
75 mm long

fits great with the Kettler Tricycle