As father of two: no, please no.
Seriously though going on hikes with my three year old for three or four hours is amazing. We only hike about as many miles, but it’s amazing how great kids are if you just give them the chance.
I find it's worst when you have chores or other jobs that need to be done in the weekend and your kids, for whatever reason, take a particular objection to cooperating. So in many ways I could see a 3 day week as potentially helping there since you'd have an extra day for chores thus could work to the children's schedule a little more. That is assuming, of course, that we don't end up with two "Sundays". (in many UK suburbs Sunday can be an absolute nightmare as everything opens late and shuts early).