At that age he's not being aggressive IMO. Dogs explore with their mouths, and they need to be taught that teeth cannot touch skin.You can try doing a high pitched yelp when he bites, and immediately turn around and ignore him, much like a littermate would. If he's really being naughty, wait for him to mouth and then give a firm NO and a TIME OUT! and put him in a puppy safe room for 5-10 minutes to cool down. He will learn that biting takes him away from the action.
I agree he is too young to be aggressive. The technique that Jane describes if administered consistently by you and the kids will work. He is still an infant and is just learning the language and expectations of a new family. Look for a puppy class near you, that will really help you. Corgis are smart and have some attitude so need positive training.
Selkie was just like this when she was that age. It does get better. For her what worked was not only a stern "no" and turning around, but I placed a baby gate across the door to the room we were mostly in and I would leave the room and not come back for a few minutes. For her if I just turned my back she would bite the backs of my legs or follow me from the room. I also used a "time out" crate (not the crate she sleeps in or travels in, but an old crate I had from my previous dog). If she got too rowdy when we were playing and bit me I would say "time out!" funny enough after a few times of doing this I would say "time out" and she would take herself to the crate plop down and look at me with pitiful, big, brown, puppy eyes.
Something else that might help would be to yelp like you're a hurt puppy when he bites too hard. Indy played too hard at first but when we did this, he learned he needed to be more gentle with us. He wanted to play, he just didn't know the boundaries. Yelping or whining will show Peanut why you stopped playing. He doesn't want to hurt you, but he may not understand.
Beware with the yelping. Every dog is different, but Nemo would get more excited when I tried yelping. With mouthing I have been religious about taking away what he's not supposed to have and replacing it with something he is allowed to chew.
Toes were a serious issue for the first few weeks. We were in a heatwave so we were always barefoot. The most important part was to not react and pull away, that would turn it into an exciting game. Not reacting is easier said than done. It's hard not to break your rules when the little bastard latches on with those little puppy teeth. Try to get away though and its all over, the herding drive would kick in. My husband took to picking him up and holding him until he calmed down (we don't have a time out area and don't want to use his crate as any type of punishment).
Toe biting has disappeared almost completely, while general mouthing has reduced a lot over the last two weeks. I attribute it largely to training. Now that he has some solid commands down, if he gets too excited I can him a command chain to distract him and give him something positive to focus on.
He has also been going to puppy play time (under 6 mos) twice a week, which I think has been good for his bite inhibition. I'm sure age also plays a factor. At 17 weeks he no longer seems to need to try to eat or chew everything he sees, only every other thing.
There were times when we were really frustrated, especially when we were tired and didn't have the energy to deal with him. But the effort has been so worth it. It is a gradual process. One morning you wake up and realize "oh wow my toes haven't been attacked in a while " Have patience and keep strong. Good luck.
Is you pup mouthing/nipping (normal corgi behavior) or snapping/biting?
When my girl was only 9 weeks old she stated to show me some very unusual aggressive behavior, which my other 2 Corgi's never showed in their life. What my Ruby would do is if she were sleeping and I would go to pick her up to put her in her crate she would growl and try to bite me...at 9 weeks! I was terrified and emailed my breeder who told me she was trying to be dominant towards me and to put her on her back and sternly yell "NO" at her. She also said that if that did not work she would glady take her back and give me another puppy. There was no way I was giving her back so I followed her instructions and it worked. The funny thing is that as soon as she stopped that behavior (about 2 weeks) her brother who was the same age ( i got them together) started doing the same thing! So I also followed her instructions on him and it too worked. They are 1 year old now and show no signs of aggression or dominanace toward me or anyone else. Good Luck!
4 kids can contribute to getting the puppy all worked up to where he cannot exert what little self control he may be capable of. Make sure all the interaction is gentle and calm and keep him on leash or separated from the kids when you cannot supervise the interaction. The other thing is to provide regular exercise (like walks on leash) to help use up some of that energy in a good way.