Well mine aren't 'grown-grown' but almost 21 and almost 17.
I think you've already realized the biggest part, you know time is flying by and you need to make the memories last. And realize what's important. I've told younger moms that it really is OK if they miss a nap, eat cake for dinner and the dog licks them in the face! Trust me as they get older, the issues get bigger.
Speaking of which, I know you can't imagine them driving since they are so young, but they WILL get a ticket when they start driving and they WILL have an accident. You just hope both are minor! Our oldest got his first ticket just 4 days after he got his license. He thought we'd go nuts! No, because he was paying for it and any increase in insurance.
We were never good at taking movies/videos of the kids but I took LOTS of pictures. Last year I started scanning and organizing the pictures which was a lot of fun and started fun conversations.
I wish I would have truly written everything down that they did or said cute, like I said I was going to! I remember a lot, and there are still things happening! But I'm sure I've forgotten a lot too.
Be involved but don't hover, if that makes sense? I've never played softball in my life! But our youngest is a competitive player. We go to every game. My husband is the official scorekeeper and I'm the 'team mom'.
Especially during the teen years, we make our home the place the kids want to hang out. I know what they are doing, who they are with and where they are! Which is more memories. Our son had 24 (25 with him) in our basement a few years ago for a Super Bowl party.
But most importantly love them, hug them and enjoy every minute!
Gosh, I"m sure there is so much more. Its a great question and I look forward to reading the responses.