Depends on the time of day. You guys would be safe roaming the parks by yourselves. There is also Disney Quest which I hear is lots of fun, though I haven't managed to get out there yet.
My big brother and I were close to that age one trip when at AK my parents went to eat at Yak and Ywt and my brother and I got our own lunch and rode some rides and everything was just fine. My advice is to either have a cellphone on at least one of you or have a set meet time.