Hello and welcome...Kim has been giving you some really good suggestions and I totally agree that you need to get a handle on the training issues right away.
4 and 1/2 months is not an age where I would be too concerned over these antics, however, you do need to find a way to teach your puppy that you and your family are top dog.
I hesitate to add this, but I feel that it is important...a crate should be a place of comfort for your puppy and not one of punishment...so looks like you do have your work cut out for you.
I agree that puppy kindergarten is the first step. Contact your local humane society or animal selter or even vet offices to find a good program. The key is to follow through with the training.
Never allow your puppy to play tug of war games with you or your children and don't let the children play too roughly with the pup either.
I am afraid that the most important factor in selecting a puppy may have already passed in this situation...a breeder should always carefully select breeding stock for temperament...if the breeding stock have agression issues, it is likely that the puppies will too.
Usually Labradooles are docile and loving...when there is an aggression factor, I always look to the breeder first. Not that this will cure the problem, but I hope that others will learn to check for this when buying a puppy.
Now, the situation is that you do have a puppy, you do love your puppy and you are doing everything that you know how to do....so what you need is some good advice and help.
As Kim has said, finding a trainer and teaching your puppy is the most important factor...proper playtime is too.
I would suggest that you look through this site, they have a LOT of good articles about all sorts of behavior:
http://www.veterinarypartner.com/
And this one is good too:
http://www.inch.com/~dogs/cratetraining.html
Please don't be discouraged...it is a daily learning process for all of us. I am still learning a lot of important lessons about raising my puppies. Take heart, your pup will be fine...he just needs some consistent direction from you and you may need some help from a trainer to get there...but you will get there!
Good luck...please don't hesitate to check in and ask questions. That's how we all learn!