I'm afraid I agree with Boiler, this is likely a non starter. It wouldn't be EB-3 skilled worker as nannies don't require any training in the US, it would be EB-3 'other workers'. Realistically, no family is going to wait that long for you to be able to start work, if they are hiring a nanny then it will be because they have an immediate childcare need. And they're not likely to wait all those years and pay all the fees when they can hire an American immediately to fulfil that need.
Plus the Labour Cert is going to be problematic, both for the reasons above, and because anybody already in America could do the job.
Which consulate? And is this for a family you're already in contact with? Are they aware of the wait ahead of you?