Mike, you might try this link, then investigate the Cox area of it:
https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=postlist&Board=75&page=1
I seem to recollect that Cox will help you with a manual if you prove ownership by giving them the model and serial number information for your mower. It should be on a sticker on the mower somewhere (perhaps under the seat?)

Thanks Redeye, that was a big help. While Mike waits for the manual from Cox he could check the mechanical situation regarding the blade clutch. I didn't even suspect it would engage manually rather than electromagnetically. Most likely the immediate problem would be that the lever is not all the way up, or perhaps the safety microswitch on the engagement mechanism is slightly out of adjustment (or slightly trashed).

Mike, if the problem does turn out to be that the blade clutch safety microswitch is not opening, you might be best advised to read the manual before you try to perform any surgery on it. The world is full of ride-on mowers that have ended up with some of their safety devices bypassed or not working. This is unnecessary and a bad idea. By following the manual you can get everything working the way it should, giving you a better chance of keeping your hands, feet and kids all in good condition.