I have 4 Quakers - 2 boys and 2 girls - and they are just like people. No two are identical and each one has their own way of doing things and looking at things. I had Quakers as a young teen in S. America and my first one in the U.S. was an early Christmas gift (totally unexpected) from hubby Fred in 2006. Much to my sorrow and heartbreak, Quaker Kiwi, died in September 2008 of pneumonia in spite of treatment as soon as I knew she was ill. Birds hide their illness only too well so by the time we humans catch on it's usually too late.
Loofa and (Miss) Daisy (aka Jaws) are girls who share a cage - both adopted. Loofa is a total doll and Daisy makes a piranha look tame. Then again the guys in my house claim Loofa is Jaws and Daisy is the doll. But Boys JJ (originally Jade) and Baby Blue are mummy's boys through and through though they each have their own way of doing things.
I don't know about stubborn but they are determined to do things their way or not at all. Offer him things you or your son eat, and I'd recommend using the word "treat" when it's something he likes so that anytime you offer something you can call it "treat" and he's likely to try it. I'm also recommending that, since your little Quaker is young, make sure he visits with your son, husband and any other resident family members so that he is used to other people and doesn't become a "one person" bird. He might still end up having a favourite person but if he's socialized and used to several people he will hopefully remain friendly to everyone.
They can sometimes become very possessive and territorial of their cage so if you can get your Quaker used to different people changing water and food it will be better for him (and you ) in the long run. BTW, does he have a name yet?
They can get very good at imitating people and Quaker JJ can imitate my laugh to a "T". Talk to your little one as much as you can and if your son talks, ask him to talk to your Quaker. They do listen and will listen to the tone of voice even if they don't understand the words. Tell your Quaker what you're doing in his cage and why. Talk to him as if he were another small child and explain things to him in a soft voice - his vocabulary will be better for it and he'll understand your tone even if he doesn't understand the words.
And yes, I guess you could say that I'm just a little biased but then that's also been said about me in regards to green cheek conures.