I applied for mine first in hcmc and then my 2 kids in taipei a few months later. Paperwork wise it's rather simple, my only hiccup was taipei wanted to know why I didn't apply for theirs in hcmc like mine. I said we were on holidays in taipei so I decided to get it done there. 500k bank statement for both, a sponsor letter stating you'll cover their expenses.

Because you need your dtv approved first before applying for your kids, do factor in a couple of weeks overseas.