Mal: You do not seem to have received much first hand knowledge of Mississauga so I'll give you a little. It has been eight years since I worked in Mississauga, living nearby, but I spent 26 years there in the police service before retiring. Your safety concerns for your children really caught my eye.
Mississauga is a sprawling, modern city. It has good infrastructure, a very good transportation system, also it contains Pearson (Toronto) International Airport. It is all very new, has excellent amenities for adults and children alike, and is very progressive in a myriad of ways. The present Mayor, Hazel McCallion, has been mayor since forever, in fact I believe she is now Canada's longest serving mayor. She leads a city that has distinguished itself as carrying absolutely no debt. The school systems there (Separate and Public) are likewise well run and responsive. The police service there is recognized as one of the most progressive and successful ones anywhere. It does, of course have many of the problems associated with a big city, but I would not have any concerns about safety there beyond concerns about anywhere else. In short, Mississauga is a great place to live and work.
The down side - it's a big city. It is congested, busy, noisy at times and yes, it does have crime for sure. If your job pulls you there, though, in my view you should not be concerned. Good luck.