I am heading in mid September with my wife and oldest son (8). I am an experienced BW paddler, but this is a first time trip for my wife and son. We are entering on a Thursday, out Sunday, and renting our canoe from Sawbill.
My current plan is to base camp on Polly. I have been up to Polly once, and then pushed south coming out at Sawbill. I would appreciate any thoughts on this plan. My main concern is that Polly is full and I’m either forced to backtrack or push on and change plans to exit at sawbill instead? Not sure if this is a real concern in mid-September, but based on permits available I am wondering. Anyways- thanks in advance for any wisdom.

I have been to Polly several times in mid-September and have always found a site (there are 15) although sometimes it has been busier than others. If you can get on the water early you'll be at Kawishiwi in about 4 hours. There's a lot of shoreline to paddle on Polly but most sites are concentrated in the center/north central parts of the lake. If you will have binoculars you might be able to scope the ones in the SW bay from the middle of the lake. They probably get used more than the one in the east arm (the one south on the west side there is not much if can find it). If it looks busy, your late, and the first one near the portage is open you might want to take it. I've stayed there a couple of times. You could check the SE bay but not many there.

I don't know how long since you've been there, but a couple of years ago you could skip the portages on the river after Square but will have a beaver dam pullover. The river has been backed up by a huge beaver dam (~6' high) just before Kawasachong to bushwhack around.

What boonie said, I think you should have no problem finding a site. I spent 3 nights on Polly last June and there were a few sites open during the week.

Personally I wouldn't take your wife and kid out through Sawbill (are you talking the lady chain?), just find a nice site on Polly and let them relax. I went from Polly to Beth on the lady chain in one day and it about killed this old man.

boonie:
I don't know how long since you've been there, but a couple of years ago you could skip the portages on the river after Square but will have a beaver dam pullover. The river has been backed up by a huge beaver dam (~6' high) just before Kawasachong to bushwhack around. "

Was up through there in May, the first one you could paddle through but I portaged it anyway to save the canoe a little, lots of rocks, the second one doesn't even exist anymore, and the beaver dams (there are two large ones now) both have well traveled bypasses now on the side. I got to Polly in 3 hours, wasn't too strenuous.