Thanx Kimbo. I guess that makes it a bit clearer. However ... now I come to the question of what Thai airways maximum measurements are for carry-on luggage??? I have 3 small suitcases, one is 48cm, one is 50cm and the third one is 55cm. Im wondering if the 55cm is too BIG for carry-on luggage - DOES ANYONE KNOW THE ANSWER TO THIS???

Yes ... I agree that probably the only time they would choose to weigh your carry-on luggage would be when they see you unable to lift it!!!
OK ... so 20kg each (Im assuming my 12yo is allowed 20kg as well???) for checked-in and 7kg each for carry-on. Thanx everyone.

Kitty