OP-I was in this same situation and believe me: it will pass. I was a nanny for this family and they moved out of state because of new jobs too. Kids were 4 and 2 yo. I was devastated for a long time. This family was so perfect and I would joke with them, saying I would be able to be their nanny only until the youngest was ready for college. They went through a bad time too, specially with the youngest, but everything worked well after a while. I still hold the family close to my heart and I know they feel the same about me. We are still in touch and I just love to see pics of the kids on social media. Today I work for a family with 2 kids too and I adore them all. My 5 year with them is coming up soon! I am having a hard time just thinking about leaving them as I move forward with my school and other plans. At least they live close, so I will be able to “steal” the kids to have weekend sleepovers at my place when the time comes.
Just know that it will get better with time. Your nanny will find a new family, you will find a new nanny, and things will get back to normal. Nothing is more important for your kids than having their parents around. They can handle and adjust to the rest. Good luck!