Where did Hobbits come from?

[Morwen]

But I think the quote I earlier provided suggests that there are significant things that Eru means to occur that are NOT mentioned in the Ainulindale, those conceived by Eru alone and only revealed at at a time of his choosing. In fact one might argue that Eru may wish to keep some of his more significant plans to himself as a way of safeguarding them. Rather than being so important that they must be mentioned, their importance requires that they should not be mentioned.

As for the significance of the hobbits, how exactly is their significance lessened by being part of Eru's specific design? I would think that hobbits as created and designed by Eru and Eru alone actually have greater significance than hobbits as a mere afterthought, the result of a latter day request by the Valar.