Because children with dwarfism have larger heads and torso's and shorter arms and legs
They ARE very late walkers.
In fact, it can be completely normal for a child with dwarfism to not walk until they are 2 or 3.
Brahm was 1 1/2
Tao was 2
and Fei was over 2 but we are not sure.
Once they walk they are good to go and many of the development questions (especially with adoption) fly out the proverbial window.