Good on you! I've found the best thing to do with upset babies is try to engage with the kid - ask the parents first(!) but babies are fascinated by new people in a way that parents can't fulfill.
Story time: I had a crying 6mth old next to me earlier this year so I pulled out the safety sheet (asked the mum if I can show him this), channeled my inner Wiggles and kick-started it with a big, excited interruption to his crying: "wow, look at the plane!" The unexpected, strange interaction short circuits their focus on being upset and he just stopped and started at me like "wtf is this dude on?". Once I had his attention I started pointing and describing all the pictures, then gave him the page. This turned into a 10min game of point at the picture, say the word or a story then hand it back. My names and descriptions for the people on the page got more crazy each time - after all, his were nonsensical too! I even got a few giggles as I kept it animated with hand gestures and big smiles. That turned into pointing out the windows or different things in the cabin.
The kid eventually got bored of the games after about 15-20 mins but had already forgotten he was upset and then peacefully interacted with his mum again for the rest of the flight. I got back to my book while he had the sky mag to read along like me and would still point out different pictures to me or check my book, puzzled why they were no pictures!
I even scored a tiny-dude high five as they were leaving which everyone knows are the best high fives.
Best flight I've had all year!