I agree that young children should spend most of their time playing. My reasons are as follows.
First of all, the development of children shouldn't have pressure. The formal education might be possible teach our useful knowledge and information. Most of schools advocate that children can have the happy learning. However, teacher can't make sure children totally understand what mean in the books. Thus, most of teachers might hold a test to examine how children learn. By doing so, this will increase their pressure and disobey school's the original idea. They are just children,
and they should have the happy memory at that time.
Second, by playing, children can learn other things. Books can offer a lot of knowledge, which includes all kind of things. However, when children play, they also can learn through this way. For example, by climbing mountain, children can close to the nature and find some interest. They can see and teach the real trees, flowers, birds, and so on. It also can spur their brain's development. This scene might appear in the textbook, but people may have curiosity to see reality about everything, let alone children.
Finally, it is precious for children to have their child's memory. When they grow up, they might memory their childhood. Some children totally study and study in their childhood. They should be unhappy because they don't have everything without studying, when other people talk about what their happy childhood. In the contrast, playing can make children have the abundant life. Their life may not only study their homework but also make a lot of friends.
For the above reasons, I agree that children should spend most of their time playing.