I agree. While it's not fair to displace passengers who selected their seat in advance, I this is likely part of the reason why Delta blocks of many seats (including preferred ones) from automatic seat assignment at T-24 for Basic Economy passengers. I'd make sure to ask at checkin and at the gate an hour plus ahead of departure time. You want to talk to someone *before* the gate agent assigns the remaining seats away. Granted I have status with DL, but I've never had an issue asking for an exit row and being given that, C+, or F on a BE ticket.

Delta surely has thought about this issue before. Given that BE is a good option for infrequent flyers (and not to mention that in many cases, getting seven seats together is a challenge in its own right), this must happen countless times a day. No one - including those who paid for MC - wants a seven year old randomly assigned next to them - so really it's in everyone's interest to have the fam seated together.

And, for what it's worth, previous posters should consider the manner in which they posted the next time something goes wrong for them. You might consider, for example, how often rules are bent and exceptions made by Delta (and probably life) for you in the past - and while you're asking for punitive 'sticking to the rule' for the OP, you have often been the beneficiary of someone who has looked the other way.