I go to the BWCA annually since a buddy introduced me to it on group and lately solo trips. I am looking for a trip a portage or two into the wilderness with sandy beach sites available for my anxious wife and young family to get their first taste of the Boundary Waters. I am shooting for late August. Any ideas?

Maybe this old thread will help?

Beaches

For an easy trip with wife and kids to beaches, you could consider Fall Lake entry (#24). A couple of NO portage options lead to very nice beaches at campsites on Mile Island, just in from the entry. If you want to cover a bit more area, the portages north out of Fall into Newton Lake and Pipestone Bay on Basswood Lake are of reasonable length for a young family, very smooth and relatively easy. Pipestone has several campsites strung along its north shore with good beach landings that are conducive to swimming.

It's true that this is a motors-allowed area so you may not have the utmost of solitude or privacy but the motor use at your targeted time of year will have diminished greatly from the peak of fishing season. When we were there at that same time of year we did not find the traffic to be too bothersome at all. In your case, to accomodate your group, the more heavily travelled/motorized area might provide a good trade-off to achieve what your looking for.

The old thread gets all that I know of, but the beach campsites on Isabella are closed due to the Pagami fire.
Hudson lake has a beach just down the shore east from the closed campsite on the north side (Pagami fire again).
There are also some beaches scattered about that are not at campsites. Such as the west side of Lake 3 and east side of Horse Lake. Both of these are marked on the maps on this site.
The one on Seagull is beautiful and big in it's own little bay. Not a secret, it is in demand. We were 2 for 3 trying to get it. Stay at the campground
or Seagull outfitters and get an early start early or mid week.

I planned a family trip last summer with my two young kiddos to Gabbro Lake. While the beach is not a campsite it is centrally located in close proximity to a handful of sites. We spent a couple days playing here as it is such a nice spot. One portage into Little Gabbro and 3ish miles of paddling to the area. Permit can be hard to come by but nice area for a family trip.

While not necessarily sandy beaches, the landings at the few sites I've checked out have been decent for swimming on Ashigan. It is one of my favorite lakes, especially for those looking for a more relaxing experience as it is a few smaller portages & more paddling though a bit less populated than some of the other just about as easy sites.

The first trip we took our five-year-old on was to Wind Lake, one portage off Moose Lake entry point. There is a nice island site there with a crescent-shaped sand beach that is shallow so it's great for young kids. There also is the classic rock shelf on the opposite side of the site which is great for lying out in the sun. The site is often taken so you need an early start. If someone is already there ask when they are leaving. Wind is a large enough lake for plenty of explores and the fishing can be good. From Moose the portage is a bit of a climb, but the path is wide and easy. You can also portage into Basswood for day trips and better fishing. The only downside of Wind is sometimes you can hear the motors on Moose as you get nearer to the portage out. Contrary to its name, Wind is not a hassle except when it is blowing a gale. If you have safety concerns it is also a quick out.