That is a myth! Actually, according to the Dept. of Justice figures, the recidivism rate is much lower than for other crimes. Everybody thinks that's true, but it's not.
I wouldn't be surprised if the rates are skewed lower because of the large numbers of false convictions during the daycare hysteria of the recent past. But, that's just a guess.
http://www.ojp.usdoj.gov/bjs/
I went to the website, what specifically shows that sexual offences do not have the highest recidivism rate?