Hi David, me again! :twisted: Its interesting that you’re playing with the mood and colors so late in the game, and if in fact its only a good thing, as you show to be moving constantly.
I’d say that the nigthversion has some unnatural touches (as the kids are lighted in a warm tone > where comes the light from? From the robot?), while it has a nice mood.
The daylight version has a very nice mood which I really can feel blowing out of it (exactly as you described it: as a perfect day for a schooltrip
), which might be more interesting to keep… So I’d vote for the daylightversion. 
I must agree a little bit on this. You might want to add a little bit of contrast on the background? (unless I’m totally in-experienced with these sort of paintings…).
I hope to see it finished soon & if I don’t see you posting before you going on holiday: have fun! 
-Gijs