A. It is good that you aren't getting angry, because if you do and this becomes a power struggle, with you trying to force him to not have accidents, things will likely get much worse.
To start with, if this is a new problem, you likely should see your Pediatrician for an evaluation and to check a urine sample. There are some medical reasons that a child might start having accidents like this, including having a urinary tract infection or being constipated.
If there is no real 'medical' reason for his accidents, then it is likely a behavioral issue.
Many people understand that an older sibling might become jealous when a new baby first comes home, but they underestimate or overlook problems that might occur as the baby gets older. At first, the new baby likely just slept and eat and you probably still had time for your older son. Now, if your 'baby' is about eight or nine months old, he is likely awake more often and takes up a lot more of your time. This might cause even more jealously and cause a sibling to regress in his behaviors, including having problems with sleeping, eating, temper tantrums, or having accidents.
Try to spend some quality one-on-one time with your older son if you think that this is the problem. You can also try to include him in your day-to-day activities with the baby, and maybe encourage him to be a helper at home. The book, Siblings Without Rivalry, might also be helpful.
Also keep in mind that he is likely old enough to talk about his feelings, and a good talk might help you figure out if this really is the problem.
If it isn't sibling rivalry, it may just be that like many preschool age kids (especially boys), he just isn't taking the time to go to the bathroom. Many children at this age don't want to interrupt their playtime by going to the potty and so begin having accidents. It can help if you begin taking him to the bathroom every few hours, on a sort of potty schedule, and not wait for him to go on his own. Lots of praise and attention for when he uses the potty and doesn't have an accident will likely also be helpful.
