Mostly teaching them. "When dad works, don't bother him". And since I do come out of the room in any case often enough (coffee/toilet/eat/etc), they saw me enough often. But it's not like single productive period is a long time, rather it's a patches of smaller events during the day.
Of course now that they're bigger, everything is a bit different.
Let me ask this directly. Is your wife watching over the kids while you get productive time?
If so, then that's not a luxury many people (including, you know, many wives) with small children have. Hence the comment that you originally replied to makes sense.
Of course now that they're bigger, everything is a bit different.