Louise is right, the procedure for removing objects from completely obstructed airways IS the heimlich for children over 12 months. In my experience, for as long as your child is small enough to 'flip' quickly and easily, thumping is the most effective. By this I do not mean thumping or patting on the back while your child is upright: gravity will only work the object further down their airway. I mean, as in infant choking, you flip your child over with his face in your hand, hold his head lower than his body, face down, and thump between the shoulder blades. Matthew still weighs only 24 pounds and is only 2 and a half feet high, (plus I am quite strong for a shorty) so he is still easy to flip. With Ayden I would need to do the heimlich. This is when you kneel behind them with one knee on the floor between their feet, circle their waist with your arms, make a fist with one hand and cover it with the other hand, and pull towards you in a J shape motion.
This is quite effective as well, but also serves to make many children puke.
It is not effective if your child is choking on something thin and flexible, like plastic, or a rubber balloon. In that case, you better phone an ambulance and pray they are within 2 minutes of your house, because you need magill forceps.
Disclaimer: the official recommendation is the heimlich for children older than 12 months. They're the experts. This is simply my experience.