It definately is possible to affect them for the good, even now that they're grown and on their own. I do not have adult children, but I grew up in a family which was very much "culturally Catholic" and not very faithfully practicing. I am very impressed with the way my mother is working introduce her re-discovered faith to my siblings who are not practicing at all. It is very subtle, for example, my brother was living with his girlfriend, and my mother was aways very welcoming to them, always invited the girlfriend to join us in celebrating brithdays and holidays, gave gifts, included them in dinner's out, and really just loved them both sincerely. That made it much easier for her to say - kindly - that the girlfriend would be staying with the girls on family vacations, or to just set up a room for her, apart from my brother's, when they stayed over at my parents. Because was so genereous and loving to them, her requirements were easily accomedated by them. It also made it easier for her to include in her gifts to them, a blessed crucifix for their apartment, and little books on Catholic living, along with things they actually wanted. When they did decide to get married, albeit not in a Catholic ceremony, my mother remembered her role and celebrated with them, though, because of the relationship they developed, she was able to talk to them about her disappointment that they wouldn't be married in the Church, but only once, she didn't push it.
This is just one example, but overall, it comes down to lots and lots of love, invitations without insistence, and massive amounts of prayer. My brother is not a practicing Catholic yet, but he is reading a lot of what my mom's given him, and he chooses to attend mass with her on Christmas, Easter, her birthday, and any special mass she might be having for a relative or friend, his wife is equally accomedating. And these a huge steps for them.
So don't give up hope, you really do still have a good deal of influence on your children, just of a different sort. Your main job now is to make sure that when your kid's think "Catholic" they think of their generous, loving, hopeful, and supportive mom.
Blessings and prayers,