I guess the question I'm curious in is, in part, what does a rank mean? Should these kids be held to adult standards now that they are out of the kiddie belt system?
Also, does a belt rank mean you have a certain amount of knowledge or are at a certain point in your journey?
As with anything... it all depends on many factors.
Take Gracie Jiu Jitsu.
Their kid program, Bullyproof, goes until your 16. [At least no test for blue belt, the first adult rank, until then.]
Their course basically starts off with making techniques/movements fun. [Games, etc. that are legit techniques/moves]
This is for ages 4-7 and up to 12. [You have to be around 6/7 before moving onto Jr. Combatives, which is basically the adult course for blue belt, but minus choking techniques.]
And there is a reason for this, as recently a 14 year old killed his 24 year old cousin by accident using the RNC. [Rear Naked Choke]
[No connection to them nor any dojo apparently for that matter - it seems they were horse playing with what they learned from tv.]
But this is why they have the structure they do... safety first.
[Gracies talking about incident]
So many factors to consider and it depends on the individual and where they are at.
For kids, I personally think that Aikido is a waste of time.
Granted, I have not seen any kids class but ours, but the whole Gracie Game idea from 4-12 [if starting] is really a good way to keep their attention, etc.
Otherwise they go through motions, get rowdy, etc. as they get bored, and it just does not seem to work. The other thing really is that its best to have the parent involved at early ages.
As for rank in general... what does it mean? Nothing. Especially in Aikido, and I do not say that with spite.
You will find with Aikido that every dojo is different in ranks below dan rank.
And even after dan rank in some instances. [As for focus, etc.]
[i.e. We have Koshinage, for example, at 3rd kyu when most start at 1st kyu]
The rank, at the end of the day, is really a mark of your own personal milestone.
In my own dojo there is a gap within the same ranks.
Aikido makes this possible, especially when there is little to no resistance and is based on theories and ideas. [Best to have someone with a Judo or BJJ background teaching, though the latter may be hard to find.. as typically it seems people transition more into BJJ and Aikido is in the background.]
note: I still take Aikido