I just wanted to post this as my own reference but also in case you in the same position. I registered my son with the following accounts because he wants to be a vlogger and we wanted to make sure he got all the accounts he could in his name. Of course most of these don't let you register them until you are old enough, so they are in fact, for the moment, my accounts. But I registered these accounts to make sure they my son (and now also my daughter) had them secured for the future.
Before you invent name or alias that you child can use as a gamer tag, vlogger name or blogging identity, consider the following:
1) It should be original enough that when a search is done it will be easy enough to find. For example the name "BrownBear" will return search results about animals and require more effort to gain traction. Instead "HairyBearBot" is memorable and likely to be easily found if searched for.
2) Check for similar names and search for accounts and websites which may also be found before you settle on a name, there are plenty of cool names that aren¡t already taken, so why use one that is.
Accounts you need to make when you start video game vlogging or gamer blogging:
Steam (Valves online gaming store)
Origin (EA's online gaming store)
Gmail (I made two accounts one for the person one for the Alias)
Youtube (I use the Alias gmail account as the youtube account for blogging)
Website (I registered a .com in the name my son uses)
PSN (account for the Playstation network)
XBOX (account for the XBOX)
Please comment if you think of any others that sould be on the list.