Where (or do I) need to report a $10.50 dividend AND some stock loss on my 12 year old sons' etrade account?

If that is his only income, he is not required to file a tax return.  It does not go on your tax return either.

But if the stock loss is large, he may want to file a tax return so the loss can be carried over to next year (where it can offset income that he may have that year).