That was the predominant belief prior to the last decade, Roy. And, children don’t want to learn a language they don’t speak in everyday life. It’s so important for a parent’s native language to be spoken at home, which is nearly impossible if the other parent doesn’t speak that language and doesn’t want to learn it.
My adopted daughter is Honduran and her ex is Puerto Rican. They wanted their two children to be bi-lingual.
While he was in college in another state and then after their divorce (there was no gap in those occurrences), my daughter and grandchildren lived with my husband and me. She spoke to the children exclusively in Spanish except when I was around. My husband speaks Spanish but the young children saw him as an English-speaker because he was usually with me speaking English. They spoke only English to me and to him, while speaking Spanish with their parents.
The kids HATED speaking Spanish. They usually tried to respond to their mother in English. She claimed not to understand them until they switched to Spanish!
Now, at 11 and 9, they appreciate the benefits of speaking Spanish and use it willingly.
Unfortunately, many parents are too stressed, busy, and tired to keep speaking Spanish to their young children. They give up or get lazy. Or, sometimes, they are trying to learn English themselves and their children are a great conversational resource, particularly if they work with people who don’t or won’t speak English. It becomes a matter of priorities — parental English is more important than juvenile Spanish. That’s life.