I believe (though I could be wrong) that daycare, extracurricular activity fees and children's camps are almost always considered S7 - no ambiguity about those.
Child care is always a section 7 if it is required by the parents so that they can go to work. After school child care, summer camps, and after school rec programs for older kids would fall into this category.
If the parent is available to pick up the child, or if they are old enough to be on their own for the full time needed, then it isn't a section 7 automatically.
Any other activities depend on the income of the parent(s). There are a number of criteria. Was the child involved in this activity before the marriage break down? Is the cost very high considering the parent's income? Is the child performing at a very high level and so would need very high level and expensive training/coaching? In short, there need to be stated factual reasons why the extra expense is justified.
If there is 50/50 shared custody then almost all expenses should be shared 50/50 anyway as a starting point, and then the question of a proportional split is addressed. The exception might be, if the child was ALWAYS at one parent's home on Wednesdays and the activity was always on Wednesdays, and the other parent was never involved, then this is an expense incurred by one parent. It should come out of their budget and/or child support received.
If there is 50/50 and each parent is in turn taking the child to lessons/practice/competition, then it is a no-brainer that the cost should be split 50/50.
Ideally there should be a percentage of disposable income calculation to say when a cost passes the threshold from ordinary to extraordinary. To my knowledge there is none. $100 per month for swimming lessons is easy for someone earning six figures; it is a challenge for someone earning minimum wage.