I found that Susie Allison of "Busy Toddler" appears to be the current person of preeminence in the niche of toddler learning/ activities/ kindergarten readiness. She has 2M followers on IG. She has a book, a website, newsletter, large IG, facebook, and Pinterest followings. NAEYC is a popular non-profit resource across multiple platforms that has four paid membership categories providing access to blogs, articles, books, online networking, and early childhood education advocacy. I also looked at accounts called "Kindergarten Readiness" and "The Preschool Toolbox" both on IG. Both give away free activities and are selling subscriptions or activity plans. Nekole Amber on YouTube is a pediatric OT who is also a parenting mentor with 202K subscribers.