In my life, there is no one who compares in love or devotion to my first full-time charge. I still love him and see him weekly!

I also think you become infinitely more bonded when you have a charge from birth onward and when you have a work-out-of-the-house employers.

Not for me, but I was part-time with my first charges, 24/7 with the second.

No one like the first. I had my first charge from birth and he is still the love of my life! I love my current charges but there is no one like the first.

Is there any way that you can just contact their parents & ask if you can see them again for a simple "friendly visit?"

If you have maintained a good relationship w/the parents then I do not see how this could be a problem.
I cannot imagine any loving parent denying someone who still loves + cares for their child to be denied the privilege of an occasional visit.

If they live far away now, you can request perhaps a FaceTime session.

Do other nannies feel this way? Of course I love and care for all of my charges, including my current ones. However, I often stop and think about the first ones I cared for full-time and wonder how they are doing. It has been two years and I still miss them terribly. I was with them for five years.