Simon,
I think that you have a fine composition, a triangle placed a little off the centre and balanced by the red wall. The light on the big girls head and hair is very fine and so is the edges and the dogs are just lovely.
I have a couple of suggestions.:
The right eyes of both girls (our left side) looks a bit flat, as if they were not rounded (eyeballs) .
The blue sweater could need more distinct light and shadow areas. Now, I think, that it is a medium value blue.
The upper edge of the leg's are totally horizontal, which I find is too much of a repetition of the lines in the wall and floor.
Also the red brick wall would benefit if you broke up the red and the mortar stripes with some neutrals to make it less isolated as a color.
Finally, for now
, I would suggest to soften the shadow side of the sleeve, at the far left, to make the edge almost disappear.
Allan