My wife downloaded this for our six-year-old and he's already hooked.
(She wrote a lengthy review last night, but it appears to have disappeared into the ether, so I'm repeating the high points). This is a high-quality app that's engaging, fun, professionally-presented, and, if our experience is anything to go by, going to boost your youngster's learning of multiplication tables.
There are three ways to learn, including a game against the clock, and the answers are designed to help you think about numbers in multiple ways. The only thing you need to note when first using is that you need to click on 'FLIP-IT' to flip over the card.
Highly recommended for any child (or adult) keen to learn (or brush up) on those times tables!