My brother and his wife did exactly this trip for this purpose last November (EWR-ORD-PEK then HKG-ORD-EWR). I got them biz class award seats. You will need to purchase a 1-way lap child ticket for the baby. It costs 10% of the 1 way applicable fare (HKG-ORD) which as I recall came to $350 or so. Small hint - you need, as I recall, to book the child ticket under the baby's Chinese name since the baby is actually traveling on a Chinese passport with US visa until arriving in Chicago when some "magic" occurs.