No, they shouldnt. Alot of kids dream big and they go over the top. Alot of kids will get upset. Like an example: if little old johnny wants to be spider man. His mom doesnt have enough money to buy him the costume and the webs, hes gonna get mad and be upset.
Yes, children should be told to dream big. If a child is told that their ideas are too wild or not possible, it could lead for their creativity to burn out. Ideas and dreams should be encouraged. A child should be encouraged to peruse their ideas & what they enjoy. One may disagree with this however, be supervised for their safety. Overall, children should be told to “dream big” to encourage their creativity & invent more.