In nursing school you'll probably have very little exposure to infants and children. Pediatrics isn't typically one of the areas that most students have much to do with other than classroom content. The nursing programs (some of them anyway) where I live don't even have peds clinicals. Not at all. The clinical experience in nursing school therefore is almost totally with adults. And as you know, there are a LOT of very LARGE adults out there. If the facilities where your clinicals are held are properly equipped with lift equipment, transfer sheets, positioning aids and adequate staff, then the physicality of the work isn't overly onerous. But the reality is that many facilities don't have any of the above. It would be worth your time to find out just how many hours of clinical experience the nursing program you're thinking of entering provides, which facilities they place their students at and if possible, what the rates of staff injuries are at those facilities. The injury data says a lot about how heavy the physical workload is. You won't be working at the same level of involvement with the patients as staff members do but you can't learn this profession by watching somebody else do it.
Now having said all that, I've been a peds nurse for 17 years. Peds patients range in age from birth to 17 years. I've seen more than one high school football player in a bed much too small for him. I saw one last night as a matter of fact. I too have a shoulder injury and chronic pain as the result of a workplace incident. There's no guarantee that peds patients will be small and there's no guarantee that there will be enough people around to help lift, turn, reposition, restrain, bathe, diaper etc so that you would be completely safe from aggravating your shoulder. Even a 10 kg baby that is sick will feel like s/he weighs a ton when you go to boost or turn. Plus, you'll be stooping, crouching, bending, reaching, pushing stretchers around, changing linen bags, carting around heavy equipment and a variety of other strenuous activities. Nurses with the sort of issues that you and I have may be accommodated in the workplace but it's very hard to go into a new job having to tell your new manager that you have a weight restriction. The only area where your patients are guaranteed to be small is in neonatal. Their equipment (isolettes, radiant warmer beds, IV pumps, monitors and so on) will weigh many, many times what the patient does. And before I forget, you will have to be certified annually for Basic Cardiac Life Support for Health Care Providers, which involves performing CPR on a mannequin, which may be difficult with your shoulder injury. I do my annual recertification and then live on naproxen for a week or so.
There are tricks that you learn over time to protect yourself. Do some more research, visit the school of nursing and talk to a faculty member, ask a lot of questions and be sure you get enough information to understand what will be involved. The choice to undertake this career will have to be yours.