A Polish Owczarek Nizinny, PON, is a wonderfully affectionate dog once it is socialized properly. It has come from a long line of sheep herding dogs that take great pride in being part of a family unit. There are certain things that bring out the loyal and affectionate nature of the dog, while downplaying some of the natural suspiciousness of the breed. The trick to socializing your dog is to start early and to include all members or your family, even other pets in the household.
Part of the success of this dog as a sheepherder was its innate intelligence and its ability to make good decisions when directing sheep away from potentially dangerous areas in their path. This also makes it a peculiarly stubborn dog that can have a mind of its own and can try to assert its dominance with everyone, including you. So, you need to be able to have a warm relationship with this dog, understand its quirks, but also be a firm and consistent owner to assert your lead.
If you get a PON puppy, immediately start to make it familiar with your family members. These dogs do not like to be alone and should be included in most of your family activities. They should be walked or exercised regularly and optimally be given some task to do, like watching a child or another small pet. They do excel in being in charge of something, but preferably it won't be you.
Obedience training is a must if you want to properly socialize this strong-willed dog. It is one thing if it wants to herd the children and the other pets in the household, but quite another when it decides it runs the household and not you. You dog should be willing to obey you, despite its instincts to follow its own initiative. This will take time and a very firm commitment to the dog. You must always be consistent with your actions and fair. If the dog thinks you aren't being fair, it can become stubborn and act out. This dog has a long memory and will be stubbornly disobedient if it thinks it is being mistreated or ignored.
The obedience training will also come in handy to socialize the dogs to guest you might have in your home. It needs to follow your lead when people call on your house because left to its own decisions it will consider everyone not in the current household an intruder. It has a naturally suspicious nature and it needs to begin to receive some exposure to strangers in your household early so it knows how to take the lead from your actions when strangers come calling.