For those who intend to do commercial portraiture the good news is that children's portraits can be lucrative. There are very few draftspersons who can competently draw children.
Soft lighting works best for portraits of children. The kid could be looking toward a bright light source. This sort of light source will illuminate the kid's face and create an introspective facial appearance. The tone stretch goes from light to medium with the eyes very dark.
Addressing the facial proportions of children in a general sense is somewhat of a waste of time. Their facial proportions change dramatically within a six month time span.
Suffice it to say that the younger the kid is the smaller the face in relation to the skull. The eyes also appear larger although this can be deceiving. A kid’s nose can be a nightmare to draw – there is nothing really to hold onto. And the mouth is extremely delicate the width of an eye. Once more, we must stress that these proportions are only a general rule and individual face proportions can be different. The above general rules can be employed for comparison purposes when you do your own careful observations of a particular face.
As always, start your sketch by striking the arabesque and then correcting the height/width proportions as necessary.
After establishing the primary facial proportions (i.e., the brow, nose, mouth, etc.) block-in the major light/dark patterns. Then, stump down the graphite using your fingers or a stump. To render and re-shape the lights use a clean kneaded eraser.
Now the features are carefully placed, sized and partially sketched. There are two points to take into account here:
1. Your pencils must be very sharp, and
2. At this point, you should never fully complete a feature. Sketch each feature no more than 50%.
As soon as the features are sized and positioned as best you can, you can now further expand them. Do not neglect the hair and sides of the face. Everything should be brought up together. As you proceed to draw you should always be on the lookout for errors in proportions and tone.
In conclusion, the fundamental processes employed to draw a kid's portrait are of course always the same. Above, we listed most of the differences in proportion and form between an adult head and that of a kid. Your mood when rendering a kid should be one that reflects the innocence and the softness of a kid.