Mine walked about 4.5 miles over the summer (she was about 4 years, 4 months at the time), but it took all day with a stop for lunch in between and some coaxing with snacks along the way. I think it can be done, but it just depends on the day, how they're feeling, energy levels, weather, who they're doing it with etc. I wouldn't assume it would be easy, but it might be possible depending on the kid and situation.
I can't get mine to walk if she doesn't want to/in a mood. I know she's capable cos she's done it before in her active phase. She's very stubborn. Nothing persuades her if she doesn't want to do stuff! It's hard
DD sometimes did a mile each way to pre-school. It was tough as she was tired. Her school is less than half a mile away and she still moans about that sometimes (although then asks to stop in the park and run around.) It’s definitely doable but there’ll be whining. See if you can encourage the scooter/bike.
Walking can be so boring. Dd states she's unbelieveably tired when faced with walking a mile, but go to the park and she's easily walk (run!) twice that. If it's something that will need to be done twice daily, what about a bike? There's bats you can get to attach a child's bike to the back of an adult bike. The journey would be so much faster.