Jessica Rolph is the CEO and co-founder of Lovevery. Here’s her tale from the field as told to Sara Kiley Watson. Popular Science’s Play issue is now available to everyone. Read it now, no app or credit card required.

When my son was 6 months old, he had a toy that always caught my attention: When you pressed a button, a purple cow would pop out, music would play, and lights would flash. It mesmerized him, but I wasn’t sure the flare was nurturing his brain development.

To clear up this mystery, my business partner and I reached out to psychologists to figure out what kids' rapidly maturing noggins crave. We found that starting around 9 months, babies have the fine motor skills to voluntarily grasp and release. At this age they’ve also started to understand the concept of “in” versus “out”—the idea that objects can be contained inside others. This is why they love to pull tissues out of a box one after another until the container is empty. Once they reach toddlerhood, kiddos become obsessed with water pouring, as that involves many layers of learning: how the liquid feels when it spills, what it looks like as it moves from one cup to another, and the sounds of splashing.

We then created toys that incorporate these activities, like a pitcher and a box stuffed with tissue-like pieces of cloth. Our games don’t just pile innovation on top of innovation or simply make noise; we strip things back to the foundations of what little minds really need.