Try and be with them as much as possible. Put the phone down, put the laptop down. Go outside, do old fashioned stuff. Go blackberry picking.
I have a DD who is 24 in a couple of weeks, my daughter is 21. Then I have ds15, dd13, dd11 and dd7.
It was definitely simpler with the older 2. No technology and worrying about social media dangers, bullying, who was following the "right" people on you tube.
Get outdoors and have picnics for breakfast on the spur of the moment. On a nice day I say right let's go to Tesco, grab strawberries, Danish, yogurts, whatever and go to the park. It's 8 am but it's a beautiful day. I still do this with my youngest 3, even the youngest 4 from time to time.
Sing in the car, all the time. Just get back to basics and spend time with them. It really does fly by. I'm lucky, ice been able to drag it out over all of these years. I enjoyed every minute of my kids younger years.
Having said all of that, I love having grown up DC too. I'm so proud seeing my DD set up home, hold down a responsible job. We go out for lunch, we go shopping, the younger DC stay over at her house. Ds is still at home but he works, buys me flowers and chocolate 😍, has lovely mates who just walk in and out like our home is theirs, just the way I always imagined it.
Being a mum has been the best thing I've ever done.