Hi,

If you want to stay in bulkhead, don't wait too long and call the company to reserve it.
We were traveling to Italy last year with our 18 month old baby and Lufthansa provided a floor bed, which is bigger than the cot. The advantage is that you have more leg room and the baby or a kid can walk (if she is walking) and there is enough room.

If you fly 4 people you could take 2 seats in bulkhead for 1 adult with baby and 2 seats in the following row for the other adult and child. However I am not sure if you buy a seat for the baby. You should be allowed to have a car seat for the baby if the bed is not available and then whatever the row is, you should be ok.