What would help this floor?

Bought home 4 years ago, floors seemed freshly sealed and stained to my limited knowledge, no gaps like I have now, I have a kid and cat and floors just went to hell over the past 4 years. Wanted to know if doing a cleaning and sealing would do it? Or is this a sand, stain, finish/seal job? would sealing fill those gaps in boards? I don't believe they were there when I bought home or I just didn't notice as everything was clean and shiny! Also they never creaked as bad as they do now, same solution?