I view Duolingo as more of a reinforcing app. I think it works better for those who know/are learning Spanish and use this on the side to enhance learning. It's a bit more difficult to use as the sole teacher of a language because they don't explain things... At least they have forums to help, but they should add in explanations too...
Well, a specific forum for each sentence is actually part of duolingo. Thus duolingo explained this to you. That's the magic of web 2.0, there is no lesser value just because someone else did it. Following your initial argument, Wikipedia does not explain anything, the people using it that do so.
Also if you speak French it would be much easier. In French "e'stos" with the accent will mean "ceux" and "estos" without the accent will signify "these" which explains that something belongs to those children or to someone. Like for example this pen is mine. Esta pluma es mi'a. (meaning the accent). When you say E'sta es mi'a, this means that the object belongs to yourself.
Here is a link further explaining demonstrative pronouns and adjectives: http://www.studyspanish.com/lessons/demonstratives.htm
Actually "estos/éstos" is used for both masculine and neutral nouns, so that translation is possible. It might not have been accepted because "boy" is niño, "hijo" is "son". http://spanish.about.com/od/adjectives/a/demonstrative_adjectives.htm
That is simply not true! In the latest revision of the language by the RAE , these words should not be written with an accent mark unless there is possibility of confusion. The same is true for solo (solitarion) and sólo (solamente). The written accent mark should be avoided unless there is possibility of confusion. This new rule is very confusing. The older rule that pronouns and adverbs need accent (irrespective of context) was a lot simpler. Who knows, the academy may change the rule again, but that's doubtful.
I am surprised to read of this change by the RAE. I think I will stick with the old-fashioned use of the accent mark. It is how I originally learned Spanish, and this dog may be too old to learn a new trick. Besides, as you say, it is easier to remember, and to recognize the word as it is being used.
This is 'children' because in English that's the most common way to say 'plural offspring' regardless of age. Offspring is a very impersonal way of describing humans, so we prefer 'children'. These may be minors or adults. They may be all male or mixed gender. If you choose to be specific about children (young age) you use 'niños'. As is the norm in Spanish, the gender rules apply.
"este/ese" becomes "estos/esos" when plural. http://www.studyspanish.com/lessons/demonstratives.htm