If your baby has a British passport, then you need either visa (for Russia) or it should be in your russian passport. As for the transportation rules they are normally the same for the airlines - 10 kg free baggage allowence and baby trolley, which can be handed in at the board of the aircraft or gate and received on the arrival even if you have a connection flight. Normall the check-in staff blocks the seat next to you for the baby (if there is space), but it is better to ask

__________________
is finally in Rostov