If a child doesn't consume adequate vitamin d, they are at risk for

The answer for this is ricket.

Ricket happens because there is a lack of calcium absorption, and vitamin d has effects on this because vitamin d helps the absorption of calcium. Calcium is a kind of mineral necessary for human body as it can strengthen bones and teeth. Lack of these can lead to soft bones, and especially in children, they may get ricket. Ricket is where the legs bend outwards.

Aside from rickets, there may be other possible deficiency symptoms and diseases such as weak muscles and pain.