Scooby, Generally, when they appear nice, they want something. Not all will be this way, but there are some that will be this way just to get what they want.
As for the kids playing w/ow's relative, I'm sure he's not thinking w/the proper "head". It's more of pleasing the ow and getting your kids use to being around her family and friends. Maybe she's babysitting the child and wants to provide that child w/some company...but I don't think I would allow it either at this time.
Find something for your children to do this weekend that will keep them super busy. Take them to the park or a museum for the day. That way, you will have a far better excuse then just saying no.
Stand your ground and do not back down if you feel strongly about your children associating w/relatives of the ow's for now.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.
