What bird species is this little guy?

Hi all, my dad found a nest inside a screener at the quarry, thank goodness he did before they started work on it. No parents to be seen for a few hours, he brought then home.

I have 3 birds that I've raised from nestling, they are up and about these days running about and trying to use their wings but no tail feathers yet. 

Does anyone here know what they are? I did think sparrows at first but now not so sure.

They are dark brown almost black on top, flecks of dark yellow. And they have yellow bellies and chest. All yellow when they gape. Pale pink legs