I think i can help you out alot southside and Rosewood, as I used to live in Hanoi for 2 years and just moved to Hong Kong from their last July....Anyways the Sofitel Metrople is one of the best hotels (my husband works for the company, accor) but Rosewood if your going for 10 days its very expensive, accor has a hotel called Sofitel Plaza(by West lake) which isnt too far from the Sheraton and is more affordible, compared to the Metropole. Also the Sheraton is a nice one (by west lake), there is also a new Intercontinental (by west lake) that is by the Sheraton which is beautiful but budget wise is in the same price range as the Metropole might be a little bit cheaper. I would only suggest you stay in hotels either in the French Quarter, or the west lake, as the Old quarter is nice to go visit but can get noisy at times, and bad traffic at times.
As far a baby strollers go, the roads are not very good in Hanoi and some areas you walk on the street so you probably wont want to use it much. For Halong Bay its beautiful and if you go to Hanoi you must take a night cruise at Halong Bay, and its not too expensive, just book it with your hotel. You dont have to go on the cruise over night but I suggest you do, as the drive is a couple of hours away from Hanoi, (I cant remeber how long the drive is sorry.)
Restaurants in Hanoi, there are so many really good ones, you have to be careful where you eat in Hanoi because of food safety issues, my husband and I go sick many times living there trying new restaurants. there is one called the Vine which is by the Sheraton hotel, good western food (but I heard that new owners took it over and it is more expensive now)
Restaurants:
Some more food safe venues are Foodshop 45 (very very afforidible and GREAT INDIAN FOOD, a meal for 2 people with alcohol cost around 15-20USD) Its by the Sofitel Plaza Hanoi, Address: 59 Truc Bach Street, Right on Truc Bach lake.
Dim Sum: If you love Dim sum I highly recommend the Chinese restaurant in the Sofitel Plaza hanoi, the Dim Sum lunch is at good price all you can eat off the Dim Sum Menu (the best Dim Sum I have ever had) word of warning if you go on a Sunday afternoon lunch it can get busy with alot of families. It can be hit and miss sometimes very busy on a sunday and than sometimes dead but I found mostly busy on Sundays. (Dim Sum menu is only offered for lunch time)
Indochine is very good and good price its the venue that Im pretty sure Neha is talking about, its got Old french feel and Vietnamese food, GREAT!Address is 16 Nam Ngu, your hotel should know this restaurant.
Oh one last thing I forgot the kids will love the puppet show to watch in the Old Quarter in Hanoi.....Also if you want to go bargon shopping the old quarter and where to go, and deal with them as they will charge a lot of money for things, ,.....Bring a calculator as there english isnt so good, you just show them the amount you want to pay on the calculator...Pay by Dong not USD!
I hope this helps