Yes and no. Technically, the forces on a rfing child in a rear end crash are the same as a forward facing child in a frontal crash. The differences are 1: rear end crashes are almost always much less severe than frontal crashes. Both cars are moving the same direction, which limits the forces, and there is usually a lot of breaking involved. (since people usually rear end someone because they misjudged stopping distance or speed, or reacted just a little late.)
Also take note, although YOU were rear ended twice, the people that hit you had a frontal crash. At least one car in every crash had a frontal, except those rare two cars backing into each other in the parking lot incidences.
2: Another difference for children,, is that a rear facing carseat being rear ended is installed MUCH differently than a forward facing carseat. the belt path is low and forward in the seat and allows for rotation toward the back window, so the seat moves with the child and doesn't pull back on the shoulders in the same way.
3: Finally, the crumple zones at the rear of cars are much more efficient at managing energy than the front of cars. The front of a car has to be rigid enough to keep the engine from landing in the passenger compartment. The back end has more flex and absorbs more energy.