What is this bird?

I know someone out there will know. I feel like I SHOULD know, as I've seen them lots of times before, but I have no clue. My step-daughter, son-in-law and the twins gave me this cardinal birdhouse, along with a feeder and birdseed for Mothers' Day. I purposely faced it toward our big front window so that if any birds nested in it we could watch them coming and going, but no luck. Then Tom told me yesterday that I had a renter. I looked at him blankly, as I had no idea what he was talking about. He said there's a bird using your bird house. Yay! What kind of bird, I ask him........a little one that flies, says Tom. See, he knows as much about birds as I do. Lol. We saw it going into the house this morning so I got a few shots of it going in and out. Then it perched on the bar that holds the house and started singing, so I got my phone and used the "birdsong ID" app, which said it was a song sparrow, except it doesn't look like any photos of the song sparrows, as they have brown streaks on their chest. At any rate, it's cute, & hopefully one of you can ID it.  :))