For something different maybe two slender mirrors over each sink

I think 2 narrow mirrors or 2 narrow recessed medicine cabinets will work. The medicine cabinet image I attached is a Broan Nutone recessed. The concrete sink image is from Mark Concrete.
A glass store/supplier can cut mirrors to any size you want.

The picture with the 2 tall mirrors is what I was thinking, but with trim around the mirrors. Or should they just be left with no trim like in the picture? The tall cabinet does have crown molding that we haven't put on yet, so I figured it would be good to put molding around the mirrors too.

Sorry, make that two. Identical.

Decide how big you want your mirror or mirrors and call your nearest glass shop. They will cut them to size and install them for you. It's not even very expensive.

Have you considered oval or even asymmetrical, irregular shaped mirrors? they may help with the space by the tower and give a glamorous look.

Framed would be more traditional, unframed more modern. A simple square cut frame like the shaker style frame on the cabinets in white would look good if unframed is too stark for you.

If you go with one mirror I think it would need to be mounted above the outlet, possibly making it too high for kids to see easily, depending on how tall they are.
I think cutting a hole in the mirror for the outlet would be odd; like it was an after thought.

I do like the look of the oval mirrors, but I was afraid that because everything else has straight lines (cabinets, faucets, sinks) that it might not look right.

two mirrors would look best. The outlet is not a big deal. I would use the put a sconce between the mirrors about head high (for an adult... they will grow up!) and simply move the GFI to the left of the sink and run another to the right of the sink. That outlet will run of the "line" from the GFI to get the same protection". Then all you need to do is refinish the small hole where the original outlet was. This would cost about $30 in materials if you can do the electric yourself. Probably $150 if you pay an electrician. Point is, I'd never let an electrical outlet decide how to finish off a project, as they are easily moved.

Use your power leads for light for a long mirror just above your outlet. Back lite with the new light emitting 120 watt chip LED light strips recessed along the edge. The other light wiring should power the hanging lights over the sinks. [houzz=]