As Gabriel suggests, restarting the iPad can often fix these problems. Most apps that 'quit' and return to the Home screen do so because they've 'run out' of RAM (random access memory). The iPad1 has 256 MB and the iPad2 has 512 MB RAM. As apps are moved in and out of RAM, the memory becomes fragmented and there is less-and-less free RAM available. Restarting the iPad initiates a process known as 'garbage collection' (it's a computer term), where all the fragmented RAM is consolidated and made available to apps.
There is an app that many Members use that performs this garbage collection without a restart. It's called XSysInfo and, if you frequently encouter this problem, it might be worth considering using this to 'clean up' the RAM occasionally.
Tim