I believe there are a lot of instances of a kid saving up his allowance, paper route, or after-school job money for a gun which is ultimately purchased by a parent. I don't think even the BATmen are going after occasional, casual transfers between family members in the same household.
Unless the kid does something nefarious, or the kid takes the money out of his pocket to pay the gunshop clerk as Dad is filling out the paperwork, I don't see this ever being successfully prosecuted.
Dad: "I bought the gun as a gift for my son using my money. That's my story and I'm sticking to it!"
Son: "Dad bought the gun as a gift for me using his money. That's my story and I'm sticking to it."
IANAL, but as I see it, unless Dad or Son commit an actual crime, or do something stupid like posting otherwise on a blog or myspace.com page, there is NO avenue of prosecution for a "straw man" purchase in the above scenario.
(What about a stay-at-home mom who buys her husband a new deer rifle? He's the breadwinner, so did she violate the law by using HIS money to buy HIM a gun?)