The best way would be to enter on your UK passport without disclosing that you are a PR. Just say you have come to visit friends. If they figure out from your name and birthdate that you are a PR and ask about that, you can say that you were a PR but left in 2004. If they don't realize that you are a PR or do realize but don't report you for not meeting the RO, you can stay in Canada for 2 years straight and thereby put your PR status back in good standing. Your SIN will have been deactivated but you can go to Service Canada and get it reactivated without a problem. You may have some problems with different levels of government asking for your PR card as proof of your status but you should be able to get around this in most cases. Some employers may ask as well.
Your children coming to visit should not flag your PR status. You just can't apply for anything from immigration. Don't renew your PR card and don't leave.
After 2 years in Canada, you can apply for a PR card again and this time, you should really think about getting citizenship. You can have dual, Canadian and UK so you have nothing to lose.
However, if the immigration officer figures out that you are a PR and insists on reporting you for not meeting the RO, you can try to talk them out of it but if they report you anyway, you must appeal if you want to keep your PR. They will let you enter and let you wait in Canada for your appeal processing which can take from 1-2 years. You may renew your PR card for a year at a time during the appeal process. However, time spent would not count towards the residency requirements unless you win your appeal. If you lose your appeal, you will lose your PR and be asked to leave. You could get your PR back but you would have to immigrate again. With the 1-2 years spent while waiting for your appeal, you may have built a relationship with an employer who wants to keep you or you may have a new woman in your life who wants to sponsor you.
