Speak Spanish Early. Speak Spanish Often.
Why Now?
The Best Time to Learn
"My children will take a language in high school... why start them this early?"
Numerous studies have shown us that language learning experiences a "critical period" in the brain - during this time, making the connections needed to learn any language is much easier than later in life.

Critical Period Hypothesis
The "Critical Period" in language refers to a section of time during one's life when the acquisition of new structures and sounds comes more naturally and easily than other times in life. While there is debate, most scholars accept the Critical Period for learning a language to be between six months and ten years old.
The following graph maps Korean and Chinese students' age of arrival in the United States with their score on a test of English proficiency.

Further Research
Second Language Learning and the Teaching of Grammar
Adults don't acquire language in the same way as young children; children are very good at learning language from listening and watching. Adults, who already have an understanding of their first language, tend to resort to rote learning of grammar as their "bioprogram" has advanced past the language learning stage.
Speaking Two Languages Increases Your Job Prospects
More on the Neuroscience of the Critical Period in Language

“Learning a foreign language and the culture that goes with it, is one of the most useful things we can do to broaden the empathy and imaginative sympathy and cultural outlook of children.”