Gidji, going for a 'trot and pop' over a couple of cross rails hardly qualifies as jumping. There is barely any added stress on the pony from trotting over cross rails at that height. It will NOT cause damage to the pony unless the rider starts getting confident and cantering him over bigger rails ;)
Hitting him as hard as you can on the head? Wow. I just got an image of a kid flinging all her effort into belting to poor ****** on the noggin. Equinphile (can't remember how to spell your username off the top of my head sorry), don't state one thing (Whack him as hard as you can on the top of the head with your crop) and then when people start at you change your opinion (Oh I meant just tap him, I said hit in case someone just tapped lightly so it had no effect). You entirely went back on your original comment. If others had not pulled you up on that comment, the OP may well have gone off and bashed her pony as hard as she could over the head. Luckily the OP doesn't appear the be that idiotic.
I think you also asked a few pages back what an egg does? It gives them a shock into thinking they've broken their skull. However it's a matter of timing as maura siad a few posts back re- hitting him on the head with a crop.
To the OP. Do not ride your pony again until you get a saddle fitter to check your saddle. You sound like you are not aware that saddles need to be fitted for each and every horse, and then, particularly with young/green horses, you should have you saddle fitted every 6 months as the horse will be constantly changing muscle bulk. If you saddle is too wide for him, it may be pushing down onto his wither and putting undue pressure along his back, and if it is too narrow it will be pinching his muscles along his spine and shoulders. A VERY good excuse to rear.
When you get on, get on via a mounting block. Even if he is only little. Mounting blocks aren't just for helping you get on. They help to stop the saddle being dragged across the horse's back as you mount. Getting on from the ground means you will be putting excess pressure on one stirrup for an extended period of time compared to if you mount from a block, thus dragging the horse's muscles across his back. Again, VERY good excuse to rear! I get on every horse, whether 11hh or 17hh, with a mounting block, and if possible get someone to hold the opposite stirrup so there is as little movement across the horses back as possible. Also avoid 'clomping' down into the saddle. Sit slowly into the saddle rather than thumping into it.