Even though your young adult children may not behave in ways you find pleasing, bless them anyway. We all respond better to a blessing than a curse. If you can remember that you wanted your child and that you want the best for your her, the act of blessing should be fairly easy no matter how frustrated you may be.
Want to know more about what this looks like at this stage of life? Check out Blessing Your Grown Children by Debra Evans. I admit that I haven't yet read the book myself, but I'm going to look for it. It has a 4.36 star rating on Goodreads so should be fairly decent.
A book I can recommend from my personal library is The Power of Positive Prophecy by Laurie Beth Jones. As far as I know, Jones has never been a mother, but she still has much to share on the subject of speaking affirmatively into the lives of others.
No doubt we can all do better in this area. And who is more important to us than the members of our family?
(While I'm not necessarily talking about this sort of blessing, I think it's nice to end with):
May you always have work for your hands to do.
May your pockets hold always a coin or two.
May the sun shine bright on your windowpane.
May the rainbow be certain to follow each rain.
May the hand of a friend always be near you.
And may God fill your heart with gladness to cheer you.