Speaking a second language
We lived in Costa Rica for a year and a half. Shortly after we moved there, my daughter (who was in kindergarten at the time) picked up Spanish and was PERFECTLY fluent in it! An American lady who heard her speaking Spanish told me she was shocked when Misty spoke English because her English was so good. (She had assumed that Misty was a native.) When we returned to the States, Misty completely forgot her Spanish (almost overnight). She's now in fifth grade. Do you think her Spanish will come back to her if she studies it in high school?
I took Spanish in high school and years later can remember some of it. Younger people generally have better memories, so it's entirely possible!
Have you thought about using both at home?