Suspended
Join Date: Jan 2015
Location: Bregenz, Austria
Programs: AA, BAEC, Alaska, Flying Blue, United, IHG, Hilton
Posts: 2,950
The mistake made was booking Basic Economy. Ok, it is a rookie error, but I can't blame the OP's family member for that. There are a lot of rookies out there and rookie errors are made every day.
"Basic Economy" essentially means "take what you get". That means it is not designed for people, who have individual needs, for example, being seated next to children, etc.
Basic Economy is designed for college students and people like me (40yo semi-retirees who just want to get where they are going).
If you care where and with whom you are seated, then Basic Economy is a bad idea.
If you want (or need) to be seated next to a child (or anyone else you care about), then pay the $20 or so (about 3 beers), to book advance seat assignments.