I had a young dog with similar problems at about the same age. After a year of trying behavioral solutions, I went back to my vet and asked him to humor me and run more tests. If we hadn't been specifically looking for a medical problem, we would have missed the very tiny red flags in his lab work. One test led to another which also came back just the tiniest bit off. Finally he had an ultrasound and we discovered that his kidneys were small. He was in early stage renal failure due to either a congenital malformation of his kidneys or early exposure to a toxin (we adopted him as a yearling so who knows what his puppyhood was like).
Frequent walks and a change in diet have made accidents in the house a thing of the past. He is now six years old and his labs still look good and we have hope that he will live the normal lifespan of a large dog and die from illness unrelated to his kidney failure.
Urinary tract infections, kidney infection, structural abnormalities, and diseases like diabetes can all contribute to a housebreaking problem. A medical work up is always recommended in a case where a pet's behavior suddenly changes, especially potty habits.
If they run tests and everything comes back as completely normal (they will likely want to do a urinalysis, a urine culture to check for bacteria, and a superchem to check the kidney function values), then a strict retraining regimen may be called for.
Some "teenage" dogs regress with potty habits even without household changes such as a new baby. In this case I would work on obedience training, nothing in life is free training, and re-housebreaking. Frequent walks, including walks after the dog has had water, food, sleep, or play are going to be important.
A belly band for a male dog may help curb some inappropriate urination, like submissive peeing or marking behaviors, as well as some leaking of urine. If the crate is too large, he may pee in it as well, so make sure your crate is sized appropriate to the size of your dog. Provide positive attention and positive reinforcement any time your dog does something he should do, even if it's laying quietly near the baby. Dogs need to know what to do, not just what not to do. Give him attention for positive things, not for negative things, and you may see his behavior begin to improve.
Confidence building exercises for an insecure dog may also help, like games of tug that he wins, or agility. If he tends to have an alpha personality, then a nothing in life is free regimen will be the cornerstone of training.
Contact a professional trainer or animal behaviorist. the ASPCA number is a good resource. You can also try the association of pet dog trainers web site for a referral to a qualified trainer in your area.
Good luck.