First errors I see are in main, you don't instantiate Child.
Lines 17, 20, 23 reference the class, not an object of the class.
Lines 17, 20, 23 you're not calling the setter correctly.
At lines 25-27, I see comments about using a three argument constructor, but I see no such constructor. Consequently, childOne is uninitialized.
At line 34 and 47, you're trying to output the result of childMsg(), but childMsg is defined to return nothing (ie void). Since you're doing all the couts inside childMsg, you should just call childMsg(), and not try and do a cout with it.
Lines 110, 114, 118, 122, you using the assignment operator, not the comparison operator. Should be:
if (gender == 'M' && inSchool == false)
Line 53, you have a default constructor for Child, but no declaration for the constructor.