as far as I know, seems like this is pretty common among children in japanese stories, declaring they will marry their parent or older sibling, but they grow out of it as they get older. or rather, they learn more about the difference between family/friendship love and actual romantic love.
(unless it is a story focused on siblins/cousins/parent-child couples, childhood friend couples, things like that. But those have those as the focus of the drama right away, or are hentai and have... another focus)
but the mother in there is acting like "she said she liked him when she was learning to write, she MUST be romantically in love with him still!"
