I find Shanghai hard work in many ways, and I'd need a fair bit of $$$ to tempt me, but I like a hit of city life, occasionally.
Don't compare it to Taiwan. Although there are obviously some overlaps, they are completely different. Go in with an open mind and it can be great.
It's hard to give a clear picture without writing stacks, so if there's anything in particular, ask.
YOU CAN VISIT ERMINTRUDE, WHO LIVES TWO HOURS AWAY ON THE TRAIN.
There is some amazing food there, despite the horror stories. You have to seek them out and you have get recommendations because the horror stories are true, but there are some great eats there. The western food, if that's your thing, is much better than Taiwan's.
Nice architecture. Chances are you won't be living in any of it, as a teacher, but there's stuff to look at.
Don't know if you see it as a plus or not, but there are loads of furriners, many of whom have stax 'o cash, so there are goods and services tailored to them. You can get your eyebrows tinted, kale smoothies, spin classes in English, and so on.
Art and exhibitions. A good local and waiguo music scene with occasional visits from giant bands.
Lots of 'third culture' kids.
Shopping is crap. Much nicer shops for clothes and stuff in Taiwan.
The underground is a world of pain.
Really shit hotpot, even in expensive places.
Shanghainese folk, are known for being rude as fuck and cheaty cheaters.
Pollution. It's nothing like those pics you see of the north, but it's not good. If your boy has any issues with asthma or whatnot, they will be affected.