How do you ask for cash from others?

I occasionally have to ask my ex for money for his girls. I feel really embarressed about having to do it and usually do it online rather than face to face. I do feel bad having to do it, but then he makes me pay for things that we agreed in the past he would pay for like ballet lessons, shoes etc, so in some ways it is ok to ask for the odd £20 here and there when I need some fruit and veg for them at the end of the month.