One Parent, One Language: each parent always speaks their own language to the child.
Mum speaks Spanish, Dad speaks English, every day. The child links each language to a person and hears both from birth.
Children answer in the language that feels easiest. Gently keep using yours, even when they reply in the other one.
The minority language usually gets less time. A busy parent may give it only an hour or two a day, so it needs a boost.
Audio stories, songs and grandparents on video calls give extra hours of the minority language without extra effort.
Play a story in the car, at bath time or at bedtime. Ten to twenty minutes a day adds up fast.