Poorer emotional regulation
Children don't have much control over their emotions. Their feelings come on fast and strong. They can have meltdowns over minor frustrations, like being told they can't have any grapes because dinner is soon. As people mature they gradually get better at containing their emotional ups and downs. This isn't to say they become stoic hyper-logical robots. It's just that if they're really sad or angry, more often than not they can pause and decide what to do with the feeling, rather than acting rashly. Less-mature people still let their emotions get the best of them.