There are two ways to design play for children in the digital age, especially if your game is products that you want parents to buy to support the learning and development of their children.
You can either: guess or observe.
Guessing is where you imagine what children need, you look at the research on paper, you think about your childhood or your children's experience and you develop an app, a digital learning environment, a toy, a puzzle that you believe will be appropriate for children.
This is a reasonable way to develop a product, it is also very hit and miss. We see a lot of apps being developed in this environment and not enough testing or iterations of an idea. We see simulations of toys and many copies of successful interactive tools. It isn't surprising many fail to meet both the creators' and parents' expectations. Young children, well they just don't give poorly designed learning tools a second chance.
With observation you need more patience. It is the skill that early childhood professional learn and enact in childcare centers and kindergartens and early years settings before most other things. And, it is a wonderful approach to employ when designing play and digital learning environments for young children.