House Sparrows nesting in my vent


I have a lovely pair of house sparrows building their nest in my bedroom vent (faces onto the street). I have read that house sparrows feed their young on invertebrates, and since I live in an area which doesn't have much green space, I was wondering whether anyone had any tips/advice on how I could help provide food for the young (when they hatch). I currently feed the sparrows suet (in my front garden, below the vent) but I presume that won't be good for the young?

Many thanks!