Probably a big day for these girls in that someone with a camera was going to take their photo. Most are wearing hats and tights, so I assume it was a bit on the cool side. Are they playing that game we call soccer? ;-)
Girls weren't officially allowed to play football until relatively recently and definitely not in those days. The balls must have been netballs and I would guess, because there are seven girls, that's a team photo. In fact they may have been a successful team because they seem to be wearing badges and rosettes.