if i cook porridge for baby at say 10am and put it in a thermal flask...then only feed it to my 9mo at about 6pm, is it ok? will the porridge go bad by then?

I think it's fine because I do that too. I cook a batch of porridge in the morning to feed twice. I will scoop the porridge into a flask immediately and leave it untouched until dinner time. Most of the time the porridge is abit cold by then...what I do is add abit of hot water to warm it up again.