English-only as well as multilingual parents desperately want their children to learn foreign languages that they will spend thousands of dollars per year on classes, books and other aids, according to the New York Times.

While no one knows how much is spent in total on games, books, DVDs, online tools and foreign-language baby sitters, the amount can easily reach thousands of dollars a year per toddler. That counts tutors who charge $70 an hour, classes for $50 a week, foreign au pairs who can cost $16,000 a year and annual tuition at private immersion schools that charge $20,000 for nine months of study.

And this does not include the outlay to retain a language as a child ages.

But as the experts pointed out, like practicing to play the piano, learning a foreign language requires more than 20 minutes a week on flashcards. At least one expert recommended children spend at least 30 percent of their time immersed in the foreign language to become fluent in it.

The most effective way for children to learn another language is through a parent or caregiver, in an immersion school or even living abroad, say linguists, language teachers and bilingual parents.

Ms. Golinkoff said preschool classes in a foreign language every day might be effective but only if parents backed that up with books in the language or hired a baby sitter who spoke the language. Popular once-a-week classes, she said, do nothing more than train the ear — at best.

To really learn a foreign language, children must spend 30 percent of their waking time exposed to it, said Christina Bosemark, founder of the Multilingual Children’s Association in San Francisco, which guides parents rearing multilingual children. She said children with less contact might understand a language, but their ability to speak it correctly would be hindered. Nonetheless, limited exposure as babies or toddlers could help if children study the language later, she said.

Experts, however, are in disagreement with the “cutoff” age for children to most easily learn a new language. The cutoff age varies from 2 to 13 years old, depending on who you ask.

Nonetheless, parents are willing to pay for private tutoring and language classes, presenting a market opportunity for bilingual speakers.