hi i went cancun this year it was a big group of 15 of us ranging form my grandparents to a 3 year old so i think i can give you some advice I hope. We stayed at blue bay club and everyone came back raving about it. The staff are amazing there and there is constant entertainment...there is a kids club that the 8 year old might enjoy but if not the staff make the pool side games enjoyable for the kids aswell as for adults but adding alcohol!! The entertainers also put on shows 3 times a week which are better than any entertainment I have ever seen they put so much effort into them and there amazing!
What else can I say it is a family resort but you do get young teenagers Im 21 and I wasnt bored at all...although the hotel is not on the main clubbing strip for the teenagers the entertainments organise night out from the hotel and the clubs are about 10minutes cab ride which is nothing. If they do go clubbing I highly reccomend basic nightclub! Bars are open until 1 in the morning and the bar staff are freindly and make good mixes of different cocktails just ask them to make you something different...I reccomend this resort especially if you are going with different age groups if you have any more questions i'll be happy to try and help you just post back.