Challenging him in chess is an easy problem to solve. Modern computer programs running on normal PCs are *extremely* strong, routinely playing at grandmaster level. This applies to free programs too - one you might try is called Stockfish.Alot of you mentioned getting him interested in chess. Funny you mentioned that, because the child had found my brothers' chess set in the closet and was IMMEDIATELY drawn to it - I showed him how to set it up and played a few games with him.
There are also dedicated computer chess sets, some of which are absolutely gorgeous. These have fallen out of favour a little as they have limited hardware capabilities and are not as strong as programs running on a fully fledged PC, but they still put up a very mean fight, more than adequate to beat even strong national club level players. And your child may find it a lot nicer to handle real solid pieces, can't beat that tactile input.