Yes. To have an inquiring mind is "normal." If you do not know, tell your child, "I do not know, but let's find the answer."
Children foremost, rather than to try to remember all of the "facts" they learn, (most of which will become outdated, or modified) need to learn to be "problem solvers."
When you tell your children you do not know, but will explore for the answer, it indicates life is dynamic. It is OK, not to know.
An inquiring mind will want to explore methods, processes and develope a knowledge base to build upon...