Sorry but there is a lot of misinformation on this thread and some of the recommendations are mad!
Labs WILL knock down a child especially in the hands of an inexperienced dog owner like the op. They could also chew every toy the children leave lying around.
Rough collie really!
Sprocker can be mad and really high energy so the early years with a young child and again inexperienced owner with not a lot of support by the sound of family advice being given. (there is little difference between dogs and bitches in any breed apart from size and the obvious! the rest is down to temperament not sex hormones)
OP dont visit any puppies yet. First step is to buy and read ]] a clear but detailed book telling you the traits of most breeds and what they are like to live with. I can not push this book enough to new owners.
Then get out and about walking in dog areas with your dc, speak to dog owners see how your children and the dogs act and look at the reality of being a first time dog owner with young children. It will be hard.
Do not go for a gun dog or spaniel, collie or staffie (unless you are experienced at looking at breeders).
Look at smaller dogs but not terriers.
Research a lot and I mean a lot, look at health issues and the tests that the breed should have and do not touch them if they have not had the tests. Kennel Club website will tell you what each breed should need.
Contact the breed club of the breed you decide on and quiz them and speak to them.
Your research could take a good year to do probably and source the puppy so be looking at how things will be in a years time in your household.