Why accent matters
A child whose family is Mexican, hearing stories in Castilian Spanish, is hearing a foreign relative of their own language. Comprehensible — but not theirs. The same applies to a Quebec family given Parisian French, or an Egyptian family given only Modern Standard Arabic. Accent carries identity, which is why the variants are separate here rather than collapsed into one voice per language.
For bilingual households
School runs eight hours a day in one language. The heritage language gets the kitchen and the weekend. The bedtime story is one of the few daily, protected, language-dense slots available — and a story the child already knows in one language is the easiest possible way into it in another.
Stories in your family's languageA grandparent's voice, in their own language
The strongest version of this is a grandparent narrating. A grandmother in Istanbul, a grandchild in Berlin — the child gets Turkish bedtime stories in the voice of the person Turkish belongs to. That attaches the language to someone they love, which is what makes a heritage language stick.
For long-distance grandparents