Boxers truly are a wonderful breed, and well worth the time and effort of raising them, in my opinion.
They are so full of life and love, and most members here would agree that they are half human most of the time.
They are, however, a lot of work. They have so much energy that MUST be given a proper outlet, and can become destructive if not given enough exercise and entertainment. You mentioned you can provide a lot of exercise, that is good. It is really not an option for a boxer, and they don't slow down much until they are 9-10 years old, sometimes not even then.
Obedience training is also a must, they are large powerful dogs and can hurt people if not taught proper manners just trying to be friendly and playful.
They do tend to be fantastic with children, although of course there are always exceptions and some boxers are not good in homes with children. They must be taught how to behave around children most of the time, it is not preprogrammed in all boxers (although it is in a lot of them!) so you must be willing to work with them as they learn. Also, you must be willing to teach your daughter how to behave with the dog, most dog/children issues are due to the child teasing/threatening/otherwise not behaving correctly around the dog. You must be willing to never leave your child alone with your dog, not matter how well behaved both of them are. Until your child is old enough to understand the gravity of their actions toward the dog and possible consequences, leaving them alone with a dog could have sad results.
Also, before you make this decision, ask yourself if you are willing to make the commitment to stick with this dog for the next 10-12 years (possibly longer, if you are one of the lucky ones) no matter what, willing to work through any issues the dog may have or acquire during their time with you. Ask yourself if you are willing to pay the vet bills that may pile up, due to illness or injury (God bless their little hearts, seems like they get hurt alot sometimes lol). Keep in mind a dog is not a piece of furniture you can just throw away or replace when you are bored with it or it gets a little worn.
Boxers are not outside dogs. If you aren't willing to make them an inside dog to live with you and your family and be a part of your "pack" please adopt a cat.
Lastly, please be sure to research a reputable breeder who does all of the necessary health testing on their breeding stock, and who show their dogs and breed to improve the breed, not a puppy mill or back yard breeder that thought it would be fun to have puppies. Or, consider rescuing one of many boxer in shelters and rescues around this country. They are wonderful dogs that suffer only from humans not willing to live up to their end of the bargain...
Sorry, I realize that is kind of a lecture, and I don't mean it to be at all. Just please be very sure you have done every bit of research and are willing to commit to a boxer. We see too many of them abandoned because people aren't willing to put out the time and effort it takes to have them. If you are willing to do all of these things, congratulations! You will never know love or loyalty like a boxer gives from any other breed (I may be slightly biased with that statement). Happy hunting for your new family member, and know that all of us here on BW are more than happy to offer advice, support, or just a listening ear if you ever need it.