As usual, ScuttleButter's advice is perfect.
WRT aggressive dogs... there were two awful attacks recently, as I'm sure you know. You probably got to hear of them through reading the papers or watching the news.
What you didn't get to hear of was news of the other eight million dogs estimated to be in the UK... because they did less newsworthy things like chase sticks and cock legs!
The very vast majority of dogs are just like mine and Scuttle's. Family pets. Forget the fact that 2 of my 3 are German Shepherds, the breed is irrelevant. What matters is that they are as daft as brushes! IME the majority of that small number of dogs who are aggressive have been either appallingly badly trained, using the wrong methods and often aggression, or they have been abused. Yes, there will always be some dogs, a tiny proportion out of 8 million, who are aggressive for no apparent reason. Breed, however, doesn't come into it.
Ask rescue... they'll tell you that they know stroppy Jack Russells and gentle giant Rotties. I do too!
I can't guarantee that any dog you take on will never bite. Nor can the Chief Executive of the Dogs Trust or even the queen. What I can tell you is how to absolutely minimise any risk - and that starts BEFORE you even get a dog.
This includes making sure that you all want a dog and that YOU will care for him when your DD has tired of the novelty. Being prepared for puddles on the floor, muddy feet, hair and walking in the rain. Being damn sure you won't get rid of him just because you are expecting/have had another baby. Being sure you can afford the vaccinations, kennel fees if needed when you go on holiday, vet bill insurance - FGS if you have a dog, get him insured. A simple broken limb can set you back many hundreds of pounds, if not more. It means being prepared to train a dog, at classes if you haven't the experience to do it yourself... and it means training your child on how to approach a dog, when to leave him alone, not to touch him when he's asleep, not to pull him around and so on.
It means doing your homework about which breed to choose... or whether you would be happy to give a mixer a good home. It entails finding a rescue, if that's the route you intend to go down, and I seriously recommend it, which will vaccinate, neuter, chip, homecheck and insists on taking the dog back at any stage in his life if you can't keep him. It means being totally honest to that rescue and going there with an open mind, prepared to let them guide you... and prepared to go in looking for a collie and come out with a German Shepherd! (After all, this is about the dog which is best for you and your family, not the dog which looks the cutest).
THEN, when you've found the perfect dog, the fun begins BUT still YOU have to put in the effort and the patience, the training, the time and the love, as do all the family. Do it properly and the risk is extremely negligable and the reward amazing. :)
Val (owner, network dog rescuer, fosterer and rescue volunteer... and nutcase!).