I nannied in Evanston (Northern suburb where Northwestern is located). I took a 3 year old little boy all over the place. We went to parks, the beach, etc. I'm sure like any big city, there are definitely areas you don't want to live, but in my experience, it was a fabulous place to raise a family. Your realtor would be a great resource as far as areas that are safer.
As someone who has moved around a lot, here is something to think about. This may not be a viable option for you, but it is the only way we would move to a new city. If possible, rent first. Find an area you think you'd like and rent a duplex, condo, house,etc. That is the only way to really get to know the areas around you. After moving to areas we thought we great, once we were settled into a house and mortgage, we slowly find areas we would have rather lived in. Sometimes it's the school district that has great tests scores, etc, but but doesn't have the extracurriculars we wanted. OR, we could have lived in a much nicer area with a shorter commute. Sure, our realtor was helpful with the houses, but to really get to know a place, living IN it and seeing what's really going on around you is the best way to know what you want. I was just talking to a friend who has also moved around a lot (even more than us) and she agreed. They no longer will just move to a place and buy a house. The last 3 moves for them involved renting first. You also aren't pressured into finding a house that you may or may not love. You have more time to find the perfect house in the perfect area. Like I said, I don't know if you are able to do this, but it sure is a great way to get information first hand. Good luck and GO BEARS!! :)