This is very sad - you seem only to meet ladies who are after your assets. Your children are your children, if the ladies have families too they should be looking after their own side of the family, not grasping after yours.
It's interesting you say that in each case you have been approached by the women, not that you have approached them - perhaps you should start taking a different approach, it sounds as if you are being seen as some sort of target!
I would stop going to dating agencies and singles clubs, just join normal clubs and societies where all sorts of people go - make a good crowd of friends with couples as well as singles. You could use that as a plan - I can vouch that it works - I met OH through being friends with his family, not by looking for a partner.