First off, it is my opinion that pedophiles need to chemically castrated.
Effect of these castrating drugs can be reversed using another easily available drugs (e.g. Viagra).
For chemical castration, not physical castration.
In fact, to prevent a pedophile like in the OP from re-offending, only physical castration will be effective. Many countries rejected idea of chemical castration due to proven ineffectiveness and waste of public funds.
But he wont be able to re-offend either way because he is in prison until he dies.
I think that people that are pedophiles and havent acted on it yet should be able to receive some kind of therapist treatment
to help them manage their urges to prevent such a terrible crime from happening in the first place