Norma I thought it was just me felt like that .
I have ds13, ds12, dd rising 9 and ds 3.5.
Looking back, the things I did a lot of with the bigger boys were: trips to the zoo, helping them set up their little wooden railway, walks around the park, reading to them.
Not enough of: playing board games, taking them out on their trikes or stabilizered bikes (still feel guilty for finding it back breakingly hard with 2 non cycling little boys in the park, and baby dd in a sling or in her pram),enjoying the moment with them iyswim. I do believe that true happiness comes with appreciating, somehow, the moment you're in, eg mentally standing back a little and enjoying your children's innocence and enthusiasm rather than simply focussing on their squabbles, mess and strong little wills.
Dd...well I'm afaid I stopped feeling guilty for what I knew I wouldn't be doing iyswim.
As for ds3...well he was seriously hard work for about 2 years - very lively and also the more children you have just the harder it is anyway blah blah blah. Now I finally have learned to appreciate the moment and I love being his parent. The best times can be really simple for him; a bus ride home rather than walking/driving, or putting him in his wellies and anorak and letting him jump an all the puddles. Equally good is sitting in the garden with a book, half watching him run, jump, climb, water the plants with his watering can etc.
Relax. All they need to remember is having fun with you somehow, even going round Sainsbury's. Maybe I'm a loon but when dd was a bit younger, 5 or 6, I'd point to someone out of hearing range, maybe halfway down the aisle, and make up some story about him or her, the sillier the better. The sory has to end when you've bypassed all the fruit shoots and haribos and reached the till though.