The answers to this question are numerous, of course, but here
are a few possibilities:
1) Childhood innocence will inevitably be destroyed.
2) The innocence of childhood should be cherished as long as
possible.
3) Our lives are a constant struggle to return to the innocence
of our childhood.
4) The innocence of children makes them more vulnerable to
suffering.
5) The innocence of childhood is only a euphemism for
ignorance.
With any luck, at least one of those will be applicable!