Does anyone have 6 year old starting to show major defiance at home?

I have 6 year old twin boys who are starting first grade in a couple of weeks. They suffered from lots of separation (from me) anxiety when ages 2-4, but not as much now. I am also starting back to work when they start school. While they are still wonderful and funny kids, I have started to see a TON of disrespect towards me lately -- and I get a "No" to everything I ask them to do. Is this one of those stages where they clash with you to make it easier to separate?