That's horrible OP, I mean airports are a pain, travelling with kids is a pain but to actually miss your flight is rubbish for you.
I've always found airport staff to be really accommodating and outbound have often been waived through to a priority queue but never asked or expected it. I find expecting the worst helps!
To your questions though..
Passengers are told to arrive at airports 2-3 hours before arrival. When I had babies/toddlers we'd go earlier to deal with the unexpected like an explosive nappy, dropped toy, stubborn toddler etc and then deal with the longer wait once comfortably through security and the toddlers were happy running up and down by the gate.
No young babies don't need to be prioritised at all, they aren't disabilities just a bit annoying! Its nice when you are waived on though.
If you need to change a nappy then it'll usually wait, in extreme circumstances (poo explosion everywhere) I guess you'd have to speak to someone.
Any baby can wait 10-15 minutes for food, noisily and annoyingly but there wouldn't be any long term damage.
Not sure about throwing away the baby food. Can you buy more on the other side ? Had you complied with all of the instructions for food ? Was there an allergy with doctors letter or something ?