Waivers generally are for negligence. You're asking people to assume the risk that you'll make a mistake or your precautions will be inadequate or not done properly and their kid (or the parent) will be harmed. You're telling them they should just not participate if that inherent risk worries them.
If you do everything perfectly under the reasonable care standard, the waiver is unnecessary since you're not liable anyway (the indemnity might be necessary, though, to cover the defendant's costs if you bring suit against them). In California, courts generally won't let you waive your right to sue for gross negligence, wanton disregard for safety, intentional actions to harm you etc, but they will for regular negligence (mistakes made when trying to do the right thing).
Attorneys often advise the group drafting the waiver to specify that the parent is waiving their right to sue for negligence. That's because your reaction is common. Many parents will sign a waiver, but, according to the court, not realize they've waived their right to sue if the soccer club or field did something the wrong way (i.e., negligently). Not sure what parents think they're waiving in that case, but people don't always put 2 and 2 together. The court will rule that the waiver was ineffective because there was inadequate information or notice about the rights they were waiving. That's why they specify negligence here. It's also because "reasonable care" is so uncertain with a new virus where transmission methods are unclear that there is a decent chance what seems reasonable care now may seem like negligence in hindsight years later when there is a trial and they don't want to fight about that.
