It is often the case that the strengths of a person’s two languages tend to vary across time. As there is more or less exposure to one language, as different people such as brothers and sisters enter the family situation, as schooling starts and peer-group relationships grow, so does the language dominance and preference of children for one of their two languages. A child may find it easier to speak English in some circumstances, Spanish in others and this may vary as practice and experience change. Sometimes the shift will be large. A child may stop speaking one of their languages while still being able to understand that language. This is a naturally worrying event for many parents.
It is often impossible and unwise to compel a child to speak a language. Sometimes, bilingual parents try to achieve conformity without conviction. For example, a parent may say to their children that they do not understand them speaking the majority language. Unless this is handled tactfully and skillfully, the result is that children learn that language is an imposition, a part of authoritarian power. It is unwise to control dogmatically children’s language preference. This is not to say that one shouldn’t try to influence it tactfully and more latently. Manipulation rather than domination tends to achieve more in the long term.
When children are younger, one possible solution is to extend the range of language experiences in their less preferred language, for example, staying with grandparents or cousins, visits to enjoyable cultural festivals, a renewal in the language materials and other language stimuli in the home for that weaker language (e.g. videos, pop records, the visits of cousins). If both parents read to, or listen to the child reading before bedtime, or if the language of family conversation at the meal table is manipulated to advantage, then subtly the language balance of the home may be readjusted.