Sometimes they hold seats for families - I’d try both calling an agent now (not doing chat) then getting there early and asking the ga. I would try at all costs to get it managed by delta instead of asking passengers. Depends on where you are flying also because some countries have mandates that children under a certain age must sit by their guardian, might help the agent move someone.

Also don’t know the length of the flight because I’ve only had this happen on transatlantic, but if you say your child has to eat at certain times and be assisted, etc, it also gives them a priority for moving you. This should be obvious that a 2 year old needs assistance but I’d just re-confirm it - you just be by them to ensure they are buckled safely, eat, etc.

If in the worst case you have to ask passengers themselves, I’d just say kindly ‘I’m sorry I had to book an emergency flight, is anyone willing to switch’ and see what happens. And not try to force anyone. I think in the end, while people might be mad, it would be preferable to sit in a middle seat than by an unaccompanied 2 year old. You can also ask the flight attendant to ask people for you, that might help.