Children are capable. Sometimes we know this and other times we doubt it. Sure the degrees of capability are great but when we are willing to be near as they approach a challenge we show them we trust them and are here when they need help.
Today's invitation to play and create involved hammers, nails, scrap art and wood. Risk is a factor. We know this and the children sense it. Sitting next to the child and assisting while allowing them to explore provides them with immediate feedback. Natural consequence. 
They may realize they need help holding the nail because they will need to use two hands to hit the nail hard enough, or that they have to focus if they want the nail to move directly downwards. When we assist with only the essential information needed to accomplish the task the teaching happens on its own. The child begins to understand how things work and that they are capable, not because we have told them but because we have allowed them.