I biked through several circles that are historic in Boston. There were challenges at many of these intersections because of the width of the intersections and the angles that folks were turning. This particular circle at Brookline and Beacon is a great example of a circle that has been recently reconfigured. Not designed for the 8 to 80 set , it does feature a bicycle turn lane that is badly faded from vehicles tracking along the dashed bike lane on either side. It was a busy intersection so there was no way to measure the width, but in riding this sort of configuration, it did provide an opportunity to take some space in order to make the crossing movement. It wasn't comfortable and I wouldn't take my 7-year old, let alone my 10-year on this sort of configuration (okay, maybe the 10-year old since she has done 2 years of Community Cycling Center Bike Camps)
The other option would have been to continue through the intersection and then cross at the signal similar to a Copenhagen left. The last one of these installed in Portland at SE Water & SE Clay associated with the Portland to Milwaukie Light Rail project has not been well used, so in this instance, it is unclear whether that's a great concept for this particular situation. It's also clear that it is difficult to communicate to cyclists what we'd like for them to do at an intersection, obviously, signage is something that can be helpful when you're in a busy intersection that you are unfamiliar with.