Wondering how this works.. say they have at least an empty seat on the plane next to you. Would UA let you bring your infant car seat on (instead of gate checking) and use it in that empty seat for a lapchild? How would you go about getting that done.. talk to the gate agent?

My dilemma is this - we're booked on a flight from EWR-ROM with a lapchild. We requested a bassinet, but I think our 9.5 month old may be too big for it (correct me if i am wrong). The plane looks half empty right now with tons of premium economy space, so I imagine the back of the plane will clear out as check-in happens. What's the right way to think about the situation?

Thanks,
- First time dad on his first family longhaul