First couple months are brutal, then the kids realize you still have to play hockey if you expect to stand out. I would suggest a clinic over summer tournaments if you are looking to ease into bantams.
for the most part it hasn't been that bad. My son took one hard, blindsided hit that he was slow to get up from but he skates with his head up so he sees most of what's coming. Most kids try to use checking the right way but there are always a few who want to play dirty and figure bantams is the green light to go ahead and do it.
Don't make too big of a deal out of it with your kid, he needs to know it is just a progression of the game. Yes, it changes the game for some but if he already skates with his head up, it shouldn't be a difficult progression.
My 2 cents, get him into a clinic that incorporates checking into other skills, Townsend, Pro Ambitions, etc. Most coaches seem to demystify checking by running a gauntlet drill. Yes, it takes the scary out but doesn't do much for form or technique. Another thing that might be important to know, in my experience every club runs tryouts differently, some will allow hitting during tryouts this year and others won't. It doesn't hurt to know this going in, just so your kid knows what to expect.
If he's on the tall side, he'll need to make sure he keeps his hands down, elbows in so he doesn't make contact with the head of smaller players. (Or he'll hopefully figure it out after a couple of game misconducts) This is a pretty common penalty early in the bantam minor season. Again, a good clinic will teach him proper form and minimize the risk of injury to both himself and others.
His positioning will change a bit, the boards are his friend now. Stay tight against them and they'll absorb most of the energy, park your butt two feet off of them like many a kid and the boards are now a danger to his health. Again, a good clinic will address this or he'll figure it out the painful way.
Last and certainly not least the clinic's will work on the above bullet points but they don't seem to address this: Late hits. If he sees a kid coming at him, he needs to assume the kid is going to hit him even 3 or 4 seconds after moving the puck so stay positionally safe and protect yourself at all times.