This is my own observation — no rigorous research to reference. But, looking at our 2 year old as he’s transitioned from a baby, I’ve been led to think about our times on, say, public transport. A baby will largely only focus on what’s right in front of their faces or directly impinging on their senses. As they grow, the vicinity becomes their circle. So if you’re on the tube, anything within sight in the carriage is fair game for them to fiddle with or want to investigate. But adults are capable of just sitting there - thinking, about things far away, in the future or in the past. It strikes me that small children just can’t do that — life is what’s around them or nothing. Hence endless fidgeting and investigation. Brilliant.