R.H.
It could be that your kids are getting older and you are missing the baby stage and the level of needing they have from mom when they are young.
God does give us signs and such, but I don't think you dreaming about having a baby is a sign.
You had your tubes tied for a reason. I think if you want to consider another child you and your hubby need to sit down and really look at WHY you are thinking you want another child and if it is right for your family at this time. Also, if you don't want to go through surgery to have your tubes untied, you can consider adoption. There are many many kids in the world who do not have a loving stable home.