The other day my 2-year-old stood up while having a bath and then slipped and fell. The tub had some thin strips of non-slip material to stand on but the gaps in between them were big enough for a 2-year-old’s feet to fit in between, so she slipped and fell. Whoever laid those non-slip strips was probably just thinking about bigger feet, not smaller feet.
Soon after, I passed a storm drain that was so high I’m sure a small child could fit through it, although an adult wouldn’t. When designing things, it’s helpful to keep in mind the lowest common denominator.