Well hello there from Hanoi!
As a resident, I can tell you this: not everything here is out to kill you :) It's generally an extremely safe city. The only thing you should worry about is the traffic, but once you get it, it's fine. I don't know how it's going to go for you here with two three-year-olds, but I don't know how anyone does anything with two three-year-olds, so, good luck to you. Don't be afraid of street food, it's delicious and safe. I've only gotten sick from a restaurant!
Here's an idea: don't stay in a hotel. Stay in a homestay. I stayed in one I would definitely recommend when I first got here, Ms. Dong's. She and her business partner, who's an Aussie, live in the house, they have a lovely housekeeper/cook and a crazy chihuahua. Look her up on AirBNB. Or there are tons of other options! Mike Homestay is an option, but not as well located and gets more of a backpacker crowd.
If you must have a hotel, and I totally don't blame you for it, use Agoda.com to book it, and read reviews. The Sofitel Metropole is beautiful and in a gorgeous part of the city close to lots of stuff. Or there are millions of small hotels that'll be fine. Enjoy Hanoi!