I think climbing gear last for a long time. Its not like you are using it everyday. I would not worry about replacing this all the time. You have to replace the rope and things like that all the time. Just to be safe.
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Replacement it is then!! Thanks for comments and confirming my doubts!

I would be weary with the rope but if you take the rest of your gear to a specialist climbing shop they will be able to look at it and tell you if it's suitable. You mention harnesses, would the harnesses that you have be suitable for 10 and 11 year olds? I think they'd be beyond full body harnesses but I do think that they'd need childrens ones as opposed to adults for a better and more comfortable fit. :o) Hope that can be of some help.

Aye, I'd be a bit wary of using those ropes as well.

Sure, they'll probably be fine in real life, but if anything were to happen......

Yes.  And No.

Experiments and testing have shown that the useful life of nylon kit, if stored appropriately, can be much longer than expected.  A good condition rope, stored well for 10 years should be perfectly adequate to hold the weight of a 10/11 year old whilst top-roping.  Some caving clubs have test rigs that can pull small samples of rope cut off the end to see how they have fared but they're basically looking at static strength rather than the shock absorption of a dynamic rope.

BUT.  All manufacturers give a five year max. shelf life for their ropes as far as I can recall.  

Dead basic rule of thumb (and I've got an 11 year old and an eight year old who climb) if you wouldn't want to take a lead fall on it then don't hang your kids off it!  Its a rule that got me to dump a couple of  ropes.....