Scratching my head at those two reversing loops jutting into the central operating/viewing area. That's a lot of your real estate dedicated to what are fundamentally scenically insincere things. Also, they are two different radii. No point in spending real estate to make one larger if the smaller radius is good enough. I would be inclined to add wyes to the lower loop at bottom and left, and get rid of the upper loop. Only one blob that way, but you still get to reverse in both directions. If you insist on two, move the upper one left to the corner.
I would also recommend building the layout as high as possible to ease the duck under. You can always add steps, stools, or platforms for the boys, and as they grow, they won't need them.
Access has already been mentioned so I won't duplicate that important design concern.
