Were you trying to charge the devices from your computer? If so, a USB socket can't supply enough power to charge an iPhone and iPad at the same time. You may want to try using the chargers that came with the devices.
Well as you found out that isn't going to work. As it is the A/C adapter creates enough power to charge one device, but by adding the USB Hub and trying to connect 2 devices creates enough of a power drop that neither device charges. If you need to charge more than one device at a time you'll need something that is designed for that, like one of these devices:
I have the RP-UC07 and it works really well at charging multiple devices at the same time. Only complaint is that the power LED is a little bright, but some friction tape takes care of that...