Lots of rest
Fighting an infection takes energy and can wear a child out. When your child's resting, he's healing. And that's exactly what he needs to do.
What to do
When he's not sleeping, encourage quiet activities. If he's old enough, read to him, let him watch a favorite video, or offer him crayons and paper or a coloring book. Teach him finger rhymes (like "The Itsy Bitsy Spider") or bring him the phone so he can chat with Grandma.