I can't tell from your post if your dog is biting in an aggressive manner or if he is being playful.
You did note that he bites the kids but "not hard." That would indicate that he is mouthing. That is how dogs play, they mouth each other, gently bite.
There are a couple of ways to stop this. I would try the first one before I try the second.
Look at how dogs react when they are together. When one dog bites another too hard, the dog yelps and stops playing for a moment.
When your dog bites, yelp. Use a higher pitch. I just say 'Ow!' The dog should be startled and stop. (think of a dog yelping - high pitched)
If the dog does not stop, use a stern voice to say 'Stop!' Don't yell. Don't make your voice high pitched. Keep it low (think of a dog growling a warning - low pitch)
Then break contact. Don't look at the dog or talk to him. Break all contact for about 20 seconds or so. If you have to, walk away. You don't have to yell or hit. That's how humans communicate.
