Could be ok. I would leave the chick where it is. Could be the last chick hatched, or an egg from a different hen. Keep your eye on them as the elders start to fledge to be sure the little one isn´t left behind without the parents. If that happens, be sure the parents have abandoned it and then go collect the bird and take it to a wildlife rehab centre. You can start looking for a centre now so that you are prepared should the time come.
I think you have to be careful about creating more problems than you solve.
If you take the smaller chick out of the nest, what happens to it? Are you confident about getting it to a wildlife rescue? If you have no wildlife rescue near you, do you know how to handfeed and prepare a wild bird for release? If you don't know how to raise a wild bird so it can be released, are you able to give a wild bird a home for life? Do you know what house sparrows' insectivore diet includes, and can you provide that in captivity?
Personally I would leave it in the hope that its simply a younger chick.