One important thing to keep in mind concerning clamperl at the very least is that many people mistake the lumps inside its shell for children. In actuality, the pink sphere is its head, and the lumps surrounding it are merely its organs. Granted, all of these are soft tissues, but clamperl is fully capable of shutting its shell before any real damage is done to them.
As for kangaskhan, rest assured that if her joey is too young to battle, then the kangaskhan herself will refuse to battle except in life-threatening instances, and believe me, it is extremely difficult to convince a kangaskhan to battle otherwise. Any kangaskhan who wishes to battle with a joey in her pouch is actually attempting to teach her joey how to battle, and she will always keep a wary eye out for any attack that may do harm to her young or render her incapable of taking care of it. This sounds like a kangaskhan is therefore at a disadvantage, but in actuality, the species is infamous for its ability to multitask. A mother kangaskhan who’s teaching her joey how to battle is even more formidable and skilled than most pokémon who battle on their own.
All of this is really important to note because in these cases, the Pokémon Association and the regional governments see nothing wrong with allowing clamperl or kangaskhan to battle. In fact, in kangaskhan’s case, preventing her from doing so is considered detrimental to her mental health and the development of her young. Joeys, unfortunately, don’t learn how to battle on their own, so they need the observations they glean from watching their mothers battle up close to figure out how to do it themselves.
With regards to any other pokémon that has young, trainers are expected to exercise their better judgment. Most good trainers never use hatchlings immediately after birth as they lack proper battling skills, but their parents are usually ready (and frequently eager) to go. Obviously, if a hatchling is so weak it absolutely needs its parent (namely in the case of illness), then a trainer is required to let their pokémon care for their young, but most good trainers will allow the parent to do this. A trainer who refuses and insists on using the parent despite the failing health of the hatchling is quite possibly abusive. However, you’ll be able to tell the difference between the average pokémon-trainer relationship and a case of abuse by looking at the disposition of the pokémon. If it seems that the pokémon is at all unwilling to battle, then that’s a good sign that something is wrong. A pokémon with young to care for will put the young first, before even battling.
In short, that’s rather kind of you to be so concerned about hatchlings and their parents, dear reader, but rest assured, both clamperl and kangaskhan are more capable of battling than you would think, as are most other pokémon with young. So for that reason, there are only really laws in place regarding general pokémon abuse but not specifically bringing young onto the battlefield.