Physical  difference is the first thing to take into account when designing for kids. Children’s motor skills (especially at a young age) are different from those of other age groups. Younger kids’ motoricts change their user behavior. For example, at early age children typically type slowly or have limited control of the mouse. This is something designers have to pay attention to when creating UI for children.

What are the unique UX needs of children?Four critical areas must be considered when designing products and services for children. Cognitive abilities Motor skills Attention span Emotional responses

"The people who are better at drawing really seem to have more developed structures in regions of the brain that control for fine motor performance and what we call procedural memory," she explained.