Echoing what others have said, suggest you buy two rabbits, as they are 'group'' animals. I think it is in Germany where is it illegal to keep a single rabbit alone. (I suppose it is not quite as essential if they are going to be inside, having lots of daily interaction with you and your family, but if you are out at work then I would definitely get a bonded pair.)
How old is your son? Personally, I wouldn't buy a rabbit for a child under nine yrs. As others have said, they are very sensitive animals, they don't particularly like being pursued, or enjoy being picked up. (And some have powerful back legs and a powerful kick.) A child has to be quite mature to understand these issues and just enjoy a rabbit being a rabbit ifyswim.
Litter training no problem. We use this with hay on top. I've only had female rabbits and mine don't smell at all. Hay does smell a bit though, although I like it!
They also need far more space than you might think. Rabbits are athletic and curious creatures. They can jump surprisingly high and twist and "bink". They therefore need daily access to an outside space.
Agree about rabbit proofing everything if they are going to live inside. Our rabbits have eaten through: a fridge cable, the cable to dh's Internet radio, the tv cables, and have knawed our skirting boards. They can't help it as it is instinctive for them in the wild to make tunnels and knaw through overhanging roots not that my dh saw it that way.
I absolutely love and adore my buns but do think carefully before purchasing! They are a big commitment and vet's bills (if rabs have dental issues) can be considerable. Thankfully, a lot of teeth probs can be prevented by providing the right diet and bits of fruit trees to knaw on etc. A constant supply of good quality hay is important too in addition to good quality all-in-one pellets (NOT the mixed muesli variety) and a fresh supply of correct veg (NOT lettuce!). See lists contained in link below.
Loads more info here. Look under 'Advice' section!
Good luck!