Thanks for the responses. In summary, I take the totality of these experiences as supporting evidence that UA is not communicating the lap-child info correctly to A* carriers on code-share flights.

I concur that LH child-related policies are a breath of fresh air compared to US carriers. I had called them well in advance of travel to request bulkhead seats with that fabulous bassinet. Even though it was a bit of a white-knuckle wait to our arrival at the gate to see if we'd be granted the bulkhead, it worked out well for us in the end.