Erin Brown does a plank, using her daughter, Lola, 2, as resistance. Start with your weight resting on your forearms, knees and toes. Next, lift up so that your weight is only on your toes and your forearms, being careful to keep your back straight as a board. If your child will do it, have him or her add resistance by sitting on your back. Be careful not to sag under the weight. You may have to work up to your child's weight.