The one with the white belt is a girl. We where just in the barn and they where jumping around Naomi's last batch of baby's where a Lamancha Nubian Saanen Boer Nigerian Dwarf mix. They are adorable.
That is normal in a way... the kids will take little sucks frequently... they typically don't stand there for 5 minutes.
It is 30-45 seconds and off they go.
Now if she won't even let them do that them she may not be the best mom and you will need to either do what you are and hope she does better or pull the kids.
Do you see any bruising or cuts or scratches on the teat or udder area that would be causing her discomfort and that is why she doesn't want them on her? Is the udder hot, red or inflamed in anyway?