Sindy, what were you expecting to get out of posting your initial message?
"I am hoping to get some advice on hiring a new nanny as we sacked ours today."
Don't think anyone has really given you any advice on hiring a new nanny. There are some general posts about hiring nannies on this board, and some of us on here know a fair bit about employment matters lets call it, so if you needed help with drawing up a nanny contract including duties, paying nannies (including possibly classing the nanny as a carer for disabled child, and thus using DPs) then I am sure we could give that - though perhaps best to start a new thread for each specific query. Also for things such as DPs posting over at Special Needs can help, as mumsnetters who post there have a lot of experience with getting DPs sorted out and know what can and can't be claimed for.
When posting on mumsnet, try to stick with facts as much as possible leaving out non-relevant information. Always better to add information to a thread, than to try to explain a situation which isn't part of the real issue at hand.
"I just don't understand why the children didn't tell us. They are very upset at losing their nanny. How can you tell if your children are covering for a bad nanny?"
To answer that question... you can't tell if your children are covering for a bad nanny (as you put it). Children will tell you what they feel you want to hear. They may have a lot of attachment to their carer and although their carer may not be perfect, they feel the situation is acceptable to them and thus they keep quiet. Better the devil you know than having to get to know a new devil!
Should you have sacked the nanny - no. Should you have given her a written warning - yes. Should you have discussed the situation with her and the children fully - yes.
Did the nanny fail to feed the children - no, not from the information provided. Did the nanny fail to cook for 3 of the children, yes - but lacking information as to why... perhaps the children never eat what the nanny cooks!
Finding a nanny who will take on the job will I think be quite hard. Not many nannies I know will take on teenagers. Perhaps this is a good time to rethink childcare plans.