4e with 1 player- and a 10 yr old at that

[Gargoyle]

Give him a pet.

A Dog that is basically a fighter (uses a Bite attack, which you can treat as a regular weapon: +3 proficiency bonus, 1d6 damage, counts as light blade). It can wear regular armor as barding.

More characters mean that combats are a little less swingy and kids love pets, even virtual ones. Making him a dog means nobody has to roleplay him.

Great idea, I'm yoinking it. And I think I'm going to let him use his healing surges to heal his pet too.

 

[Gargoyle]

You could also give him an elite template: +2 defenses, +2 attacks, a special bloodied encounter power as a minor action. I like the idea of giving him second wind as a minor action and I like the idea of giving him an action point every battle.

The elite template is also a good idea. I've run a bunch of sessions, and they've just hit 3rd level, and even with the extra action points and second wind as a minor action it's still a little deadlier than I'd like since there are only 2 of them, so these ideas might be the edge that my two players need.

Of course, if I let them both have pets and an elite template, I may swing too much in the other direction of making them too powerful. However the wonderful thing about 4e is that it's so easy to add more monsters if things get too easy.