For the two-language trick to work, both languages need to be equally useful for the kids. My sister and her Canadian husband tried having her speak to them in

For the two-language trick to work, both languages need to be equally useful for the kids. My sister and her Canadian husband tried having her speak to them in Norwegian, and him in English, but as soon as they understood that she could speak and understand English, but he could not speak or understand Norwegian, the kids switched to English. They still understand Norwegian, but they speak little of it and with a heavy English accent.