We need to trust that the facts, concepts, and explanations that we get from the people around us are generally truthful. There is so much to learn, that when we are exposed to an idea our default is to believe that it is true.
Little kids like to help out. An easy way to engage a toddler in play is to start to work on something and make it look like you need help. Often, they will come over immediately and work to help you with whatever you are doing.