As a rule, it is best to provide children with models of correct Spanish through contact with native speakers, books, audio books, video, and music. With sufficient exposure to Spanish, they will learn the structures of the language.  They do not need grammar explanations.

Adults, however, often appreciate some information about grammar.  The explanations on this site are very general and brief.  If you are interested in learning more about Spanish grammar, there are many excellent websites with detailed explanations and practice.