Can you start a journal? And start observing and write? That's what I did when I worked in centres. It is helpful to parents and also medical practicioners.

Record when usually happens the accidents and time. And what are his activities and what he eats. Record that information for about three days and you will see. Also notice how he behaves before the accidents and after.

Some times children can not express verbally what is botherig them but they do through their actions or behaviour.

If you find that his accidents are a routine then target those with reminders. If it is b.m. constipation then usually they become aggressive or unhappy. Then you can target that with a balanced diet plan, another think is at times they ignore to go to the bathroom because they are over stimulated (new toys, tv etc). If he cries constantly, tells you something is not working right.

And remember, their bodies still developing and that can also be the issue.