Need help with lots of bug bits

I need help solving a frequent bug-bite problem. My young child gets lots of bug bites (dozens), seemly every day or so, and I can't find the cause or get it to stop. I have:

• Pulled up all the carpet and padding so there are only hard-wood floors.
• Sealed the window.
• Sealed/used gap-filler on all the edges where the wall meets the floor.
• Switched out the mattress for one from a hospital, which is sealed and hypo-allergenic.
• Applied repellent spray on all edges, corners, and cracks.
• Vacuumed regularly and always switch out clean sheets/blankets.
• Treated all pets in the house for fleas.

I believe it is isolated to this bedroom because all other members of the house use all other rooms and furniture but nobody else is suffering any bites at all. However, I am at a loss as to what could be causing it. All I can think of left is:

• The hardwood floors that now remain, having pulled up the carpeting, do have tiny cracks between them. Perhaps there is something underneath this specific section of the house (crawlspace)?
• Could something be coming in through the HVAC? If so, why is it so regularly making the adventure to come out and repeatedly bite this child?

I suppose I could still try:

• Covering the floorboards with some kind of sealing paint.
• Bombing the room.
• Switching rooms with the child.

I really need some insight, I'm at a total loss. Why only this child and why so many bites so frequently? I've investigated other environmental sources and it doesn't seem to happen at other houses nor is it coming from school as no other child suffers.

Does anyone have any ideas of what I could try to not only determine how/why/where this is happening but also how to stop it?