He added: "We are absolutely committed to continued to adjusting and meeting these problems. If we don't, consumers aren't going to do business with us."

Capcom and Recharge Studios both said Apple bears some responsibility to build safeguards into iOS. Capcom's Larson noted that a customer's account remains logged in for 15 minutes after downloading an app or making an in-app purchase--making it possible to download further content without re-entering a password.

"This is not unique to our app; this is a function of iOS and we have no control over it," Larson wrote, and added: "If parents think their child may have purchased in-app content by accident, we encourage them to request a refund from Apple."

In its statement on the matter, Recharge Studios suggested that one solution is that Apple require a fresh password entry for each in-app purchase.

Apple spokeswoman Trudy Muller declined to comment directly on the FTC inquiry. But she noted that parents can prevent many problems before their kids ever get ahold of the iPhone. "A password is required to purchase any good from the App Store, including using in-app purchases," she said. "Parents can use our parental control settings to restrict app-downloading and turn off in-app purchasing."