We carry lots of evolutionary baggage with us. For millions of years, children have been sitting on their mothers' hips all day. Lying around somewhere on their own for a lengthy period of time would mean they had been left behind in the high grass of the savanna.
The only way for children to survive this would have been to be loud enough to be heard by their mothers, and for the mothers to be eager to find and pick up their children. A couple hundred years of civilization, and a few decades of strollers, won't change this.
So follow your instincts and pick up your child. These instincts match with those of your children.