Most Helpful Guy
It sounds like his new girlfriend is taking an interest in his family and trying her best to help. Women are far better at shopping for clothes than guys usually are. If she's willing to take that on as a new girlfriend, that's up to her.
You can take at least one thing into consideration, you won't be paying for new shoes or some clothes the kids may get. I saw your comment that he doesn't care about their grades or school work.
You can get mad all you want about him giving new girlfriend the kids clothing sizes, but take consolation in that he's doing something for the kids, even if its through his girlfriend. He may not be trying real hard to take care of his own kids, but at least something good is being done for them.
Most Helpful Girl
No, its his girlfriend and she's interested in his life. Mind your own business