All the chidren are boys.

EXPLANATION:

Because there is a dichotomy of boy versus girl, any given solver is likely to assume that if half of the children are boys, the other half must be girls; but with an odd number, this is untenable.

Accordingly, as soon as this assumption is discerned as fallacious, one can arrive at the precise solution to the given problem.

Since, 3.5 does not make much sense in practical terms, it follows that ; all the children are boys , half of them are boys, and so is the other half.