I'm old, but I do remember the kids being little. They were close in age, 1985, 1987, 1988 (88 has OOPS for a middle name!), and to be honest, we NEVER worried about them having 'alone' time with a parent. It just happened.
Went to the grocery store with one, while another was at preschool and I have to pick them up in a half hour. Waiting in a doctor's waiting room, waiting. Going to the zoo, as a group. There were always things to talk about. Having conversations with Mom, when treated like what they say matters is better than alone time.
At that age, they loved 'helping.' Sweep the floor, put laundry in dryer aa I take it from washer, etc. Picked up to push the button. Sometimes I made up stuff, "Can you sort these tupperware bowls and match the lids for me?"
Little things, with Mom or Dad, they love, just attention.
25 yr old memory:
I was in the checkout line at the grocery store. As usual, one in the seat of the cart, the 2 older holding on to it's side. A man ahead of me, looked to be about the age of my Dad commented, "Your family makes such a lovely picture" I can't even remember all the times a complete stranger would come up to me and tell me how they admired my family.
The kids weren't doing anything other than going out with Mom. Little kids just like that kind of stuff, and they are all somewhat close now, I think, because we did so much together.
Also, it was important to expose them to all sorts of things, letting them decide who they were meant to be. We have 3 very different adult kids now, who seem to be secure with who they are, but seem to appreciate their differences.
1 is married, 1 engaged, and 1 is busy. All bought homes before they were 30, and are in the 25% tax bracket, 1 spent 6 years in the NAVY, so the way they were raised, though of course not perfect, must have not been that bad.
IMO, it might not have been alone time, but it was quality time