1. Take blood pressure when the child is calm. If the child is fussy, irritable, of moving their limb at all, you are going to get an abnormal reading. Swaddle the baby, hold them, give them a pacifier, etc. to calm them down before you try to take their blood pressure.
2. You apply a blood pressure cuff the same way on the leg as you do the arm. But rather than lining up the arrow on the cuff with the brachial artery, line it up with the posterior tibial artery.
3. Make sure your cuff is an appropriate size. Too small or too big will give you abnormal reading. If you're unsure about a result, recheck on a different limb or with a different cuff.