Blue Tits

Hi its been a sad day today. I had 3 baby blue tits nesting in my bird box, 4 days ago 2 of the babies left the birdbox and settled under a bush at the bottom of my garden, but there was one still in the bird box and it kept calling for its parents but they didn't come to feed it, I was getting concerned so I took a look and the poor little thing was smaller than the others and I could see that he was very weak  within an hour  he was dead. Then to top it all yestarday one of the other babies went missing so now there's only one left,  which the parents was doing a good job coming.back and forth with food he's was doing so well. Then today a bird took him as he was perched on a plant pot, it was very upsetting to see. The parents came back over and over calling and looking for it over and over, then by this evening they stopped. I now realise what a hard life these small birds have poor things. Here's two questions! Maybe someone can answer will the mother lay more eggs this year? and will they use my birdbox again next year as they did this year