Most lines not do not accept children under 12 months as they have no facilities for neo natal care. This is a paste from P&O's website......Children aged 6 months or less at the commencement of the cruise will be refused permission to board the cruise ship and P&O Cruises shall have no liability whatsoever for any consequences of such refusal. Certain cruises also have prohibitions on children aged 12 months or less. Passengers should check with P&O Cruises before booking.
I did take a 6 month baby on Oriana (but it was 11 years ago)!. Like Wilba said check PO Brochure for terms and conditions as some lines now only accept babies over 1 year, although I am sure that providing its not a long haul fly cruise P&O will accept 6months. Oriana & P&O was great, like you I was with a large family party, so plenty of support. I was able to preorder all my baby food and juices (even milk) if you are not breast feeding, before we sailed - this was then provided for me in a designated cupboard in the dining room for me to take as and when and what I needed. The childrens playroom also provide things like bottle sterilisers etc (As I said this was 11 years ago) so perhaps someone can clarify that this is still the case. The night nursery was fabulous and provided you can get baby settled you can leave and enjoy your evening meal in peace. You can go into the playroom with baby and provided you stay with them you can make use of the toys etc. There is a little splash pool just outside the playroom - all in all I cannot fault P&O for their childrens facilities.
The p & o ships are well equiped now for young families, even 6 month olds are catered for on these ships, early mealtimes, nurseries, and excellent babysitting if needed, also all of the ships have nannies, if you need to have your baby cared for, they will give you a pager, and call you if needed. i have just come off of ventura, and there were many under 1 year on board. contact p & 0 direct, or travel agent, i dont think you have much 0f a problem.
I am planning to take my 2 year old on Oriana in July. I have previously used the Night Nursery on Ocean Village 2 (when he was about 7/8 months) and thought it was a fantastic facility and the staff were great. They were extremely accomodating and leant us a bottle warmer (I took sachets of baby milk in powder form). The restaurant also had jars of Hipp baby food. I cannot imagine this being much different. I don't think you'll have any problems. The only thing I'd advise, is a small stroller, as there is limited room in the cabin once the cot's between the beds!!!