I have a WW1 era German “pickel” helmet that is so small it must certainly have been worn by a child. It has a big dent right in the front of it that looks like it came from a butt stroke.
They don’t call Germans “squareheads” for nothing. Most WWI or WWII German helmets I’ve seen seem quite small.
That dented pickelhaube was made of leather & the M1916 `stahlhelm’ partially solved the problem.