The RasPi 2 with its quad-core processor may use a lot more current than a RasPi B+. Actual current depends on what the CPUs are doing, and what USB peripherals are powered through the RasPi. 1A current is probably enough for most users, but some RasPi 2 applications may need more. A 700 mA charger is marginal. You also might have a problem with the Micro USB cable: many of those have very thin conductors which can cause a significant voltage drop at 1A. Unfortunately, it's hard to tell what you're going to get with most USB cables.
I'd try a phone charger like John Alexander suggests. If that's not enough, Adafruit has a nice 2A power supply with a good USB cable. I haven't tried that particular supply myself, but I've had good luck with Adafruit.
Thank you very much for your replies John Alexander and John Beetem. I am looking into this as a Christmas gift for my sons. Glad to know that a separate power supply is needed.
