That quilt is beautiful! It is very girly so what I would do is to add accessories in blue and green matching the blue and green from the quilt. That way it downplays the pink a little. Also move the flowers on the wall to her side of the room , and find something similar but boyish for his side of the room. Again, try to find them in blue and green, so you don't introduce new colors.
That would be my advice. Hope it helps