I would not think there would be any health hazard - burned wood does not give off ay fumes. Other burned materials that may give off fumes would only do so while they're burning. Once they have stabilized, they should not continue to release any new chemicals.
If you're constantly stirring up residue from the fire - like knocking loose ash when you bump the walls - you could be breathing in airborne particles - still, no chemicals.
And if there had been pressure treated lumber used anywhere, you'd want to make sure the ash from that is not still kicking around (like near the play area.)
Rebuilding burned houses is fairly common - I've never heard of any health hazards associated with it.
You might try the Indoor Air Quality Information Clearinghouse service of the EPA: http://www.epa.gov/iaq/iaqinfo.html (800) 438-4318