IMO, UA should start blocking more seats like DL does for reasons like this... UA does block 4-6 seats [usually two seats in the bulkhead and the other 2-4 further down the plane], but that is mostly for accessibility reasons and certain disability accommodations. However, I think they should start blocking about 15-20 seats on the widebodies, so the airport agents have more wiggle room in accommodating people with various needs. This will make the GAs lives easier and significantly reduce the odds of a parent being split from their child/children.

DL blocks all bulkhead seats and the last row or two in Y as well as random rows throughout the plane.