Question: what is the answer to cuantos anos tienes?
Answer: For example, if the child is 5 years old, he would answer your question by saying, Tengo cinco años. You can also say the age of another person, as in the answer to the question, ¿Cuántos años tiene tu hermana? If the child's sister is 10 years old, he would answer your question by saying, Mi hermana tiene diez años.