My kids won't sit still. We encourage you to let kids be kids. Provide them with props and toys and let them have a good time in the studio. The expressions made and the actions that occur make for priceless portraits that truly reflect the personality of your child. The Kids Gallery displays samples of some great portraits of children.
People have a natural tendency to make themselves comfortable.
Unfortunately, relaxing one's muscles leads to poor posture. Poor posture leads to rounded shoulders and double chins. To look one's best it is necessary to win the battle with gravity. Professional photographers are profficient at proper posing, lighting, and composition and are quite capable of seeing you at your best. Personal tastes dictate the type of portrait you might consider.