USB ports and charging iPads etc

Hallsontour

In the caravan Magazine this month (March) they talk about fitting some USB ports in the wall to charge your phones and iPads with rather than using a plug. Good idea I thought but my daughter informs me that her iPad has a higher charge requirement than our mini iPads or the iPhone's. If I fit a USB port, or buy an adapter off a well known website that plugs into a normal socket with 4 USB ports in, can I still safely charge all of our i-items or am I best just using the charge leads as supplied as we do now? 

Thanks for any helpful replies