As you know, that’s not true. There are plenty of children in the US who are fluent in Spanish and English. Then there are millions more fluent in Mandarin, Cantonese, Vietnamese or Thai. All of these children have something that mono-linguistic children don’t have.
They have a foot in another culture. A culture who sees things in a different light tastes different flavors and may even have a different creed. Giving children the possibility of language classes philadelphia is not giving them a huge difference or a step up, it is leveling the playing field. It is giving them the same advantages that children who start bi-lingual already have.
Although it is hard to believe, you might have the smartest child in the class now, but that advantage will shrink over time, and without a second language there will be others who are more attractive to an employer.
Learning a language as a child is much easier than learning one as an adult. Children don’t have preconceived ideas of structure or grammar. Using a separable verb is just the way it is done and they don’t need to think about. Having two words or even three for everything is not a problem.
There are stories of children where their mother talks in one language, their father in another and then there’s school and daycare where they speak English. Children with this language input are slower to speak, but when they do, they are bi- or trilingual.
This is a huge advantage in the long-term. This world is a small one. The number of Americans who have a passport is increasing all the time. The rest of the world will not let us skate by with English only for much longer.