Double charges for iTunes store purchases with my child's Apple ID

When I purchase music for my daughter, on her device, why am I consistently being double-billed for song purchases? It does not happen with each song, sometimes only 1 song out of several are double-billed, sometimes all of them. The purchases are made on her device, under her ID, which prompts me to approve, which I then approve. However, some songs are billed once under her ID and again under my Apple ID, so that I am being charged twice. While Apple has provided refunds, it is a hassle to have to go through this every time. Is there any way to prevent this, other than purchasing under my Apple ID and then having her download to her device?