All transit points through United hubs (SFO, LAX, ORD, EWR, IAD) have different problems for babies. LAX: TBIT to T7; SFO, International (G) to either E or F; EWR: B (could be C) to C. ORD: M to B/C (shuttle). Based upon the relative length of the two flights, Swiss (LX) to either LAX or SFO and then a short-hop flight on United is a good choice. Both LAX and SFO options have long layerover time.
There is probably a thread about bassinet.