To me, 24" is the minimum. When we have large dinner gatherings and need to squeeze more than 14 at the table, I squeeze down the 24". It's uncomfortable to me. In your situation, 6 y.o.'s quickly become large, gangly teenagers who take up much more space than a child. Even my 7 y.o. needs 24" or more for homework. If he were doing work side by side with another child (like DS at school at their little tables) someone's work will always be in the way of someone else (like in DS's class).

If possible, I would aim for 24". You certainly could get by with less. The world won't end if you have 20", but IMHO your life and those of your kids will be less stressful later at this work area if the minimum is met. Can you post your layout to see if it can be tweaked?

Can you add a fold-out leaf? The 6 year olds are not gonna stay small or even cute ya know!

Growing up, we had a counter with stools where we sat for some meals and more often for homework, drawing, etc. When my brother and I were smaller, we could fit four stools comfortably. As we grew up, we no longer could fit all four of us at the counter. I don't have the exact dimensions, but I can conclusively say that when kids are younger, you can squish them into a smaller space than adults. But as fori mentioned, they aren't going to stay small. So you'll have to accept that if you compromise now, you may not be able to fit them anymore as they get older. And adults may not want to sit in the space if they do not have sufficient room.

I don't know if this will help or not. Recently I had a similiar question. We rounded one end of the island based on help from GW. Attached is the thread with all the details. I can't say for sure how its working as we don't have stools yet.

Here is a link that might be useful: help with island seating

I have 102" of counter seating on my peninsula. It seats 3 with room to spare and one on the end. We added a 4th stool to the run and it's still comfortable (25.5" per stool). Our stools came in sets of 2 so I sometimes put the 6th on the end (38", so only 19" each) or along the long run (20"). It is tight, but doable for smaller children.

Imagine being on a plane with 24" seats for a few hours.

You are not talking about a dinner table, but casual seating for mostly kids, so I sure don't believe 24" to be the minimum in those cases you describe. We had 5, and in a pinch, 6 stools, in a 7 ft run of raised counter bar in our last house. It worked just fine for use like you're talking about. I imagine that when the kids got older and larger, it would've decreased to 4, sometimes 5 stools instead. 4 in that 7 ft would've certainly had comfortable room for us.

In the house before that, we had a 5 ft bar with 3 stools. That was fine for kids' meals and casual adult seating.

It also depends on the width of your stools and if they have backs. We have backless wooden stools in the latter situation and had backless padded stools for the 7 ft bar seating...So about 14-17" wide each.

I think you have to consider the body-size of your family.
My kids are still young and small.
Two adults are on the slender side.
Our family and friends are not overweight.
I can see if most of my family and friends was 50lb to 100lb heavier, we would only fit 3 versus 4 people at our counter.

We have backless seats, which take up much less room.
getting in and out of seats are easier when the mass of the stool is less; ie no backs.

We have backless padded stools ... 4 on a run of 72", so 18" per stool. We normally leave the stools set up like that when no one is sitting there. For about 65" or so the stools pull up to the overhang off the back of the cabinets. The last 7" is overhang off the end of the cabinet run. When we need to, when seating adults or just when we want more elbow room, we pull one of the stools around to the overhang end, which puts 3 stools on the run and 1 on the end.

We had four stools on a 6' run growing up... 2 kids and 2 adults, and then the kids became adult sized. It was still never a problem. One important thing for us was that each end of the seating overhang was open so dad's knee on one end and brother's knee on the other could hang off. The corner was rounded ever-so slightly so it wasn't a problem. The stools were simple stools with no backs, and recently my mom has upgraded to 3 larger stools, but the 4 worked well for us.