I was on a little league board. In my state, we had pretty strict background check requirements, and those providers were the “trusted partners” that were given sensitive information. Now, little league volunteers are mandated reporters in New York, so the government gets information for training enrollment.
The school enrollment information was used for eligibility... the eligibility requirement was to live or go to school in the territory. It frequently came up for kids in private school outside the zone or kids in shared custody arrangements. There are many edge cases, especially with shared custody, foster or arrangements where “easy” forms of required information just isn’t available for various reasons. Most “nuclear” families provided a birth certificate and any letter from a utility, bank or tax bill.
Age is very important for leveling kids appropriately and keeping them safe, which is why birth certificates are required — parents are insane and go to extreme lengths (I personally encountered forged documents, parents who delayed entry into kindergarten to age 6, bogus documents from siblings or cousins, etc) to try to let older kids play in younger levels. It’s a hazard for an 11 year old to pitch or hit against 8 year olds. Little League is used as a way for folks to get kids into elite travel teams, etc.
Marketing stuff was totally different and may vary by league. We wanted all communications to our folks to go through and be approved by us. “Bob the plumber” could hand out flyers, get an ad or have a blurb in an email campaign. The big companies (currently GM, Gatorade, Honda in my region) just push materials down and use contests to get personal data.