There is a very good reason to NOT have the death penalty for child rape: It gives the "child abducter" type some reason not to kill his victim when he is finished with him or her. For some that won't matter, but I think that there are abducters who are organized and rational enough to plan to minimise the penalty if they are caught. Pedophiles cetainly do go to the trouble of traveling to foreign countries where the penalties may be less severe.
It is very difficult to settle on a "proportional" penalty because all sorts of different actions are lumped together under the same offense. There are boys convicted of a sexual offense against their girl friend when their ages just straddle some age boundary, in the context of a loving and consentual relationship. There are older men taking advantage of a teenage girl's inexperience, but again with consent. There are true pedophiles who gently cultivate a preteen to seduce them. There are authority figures who convince children to submit. Then there are the abducters who grab a child, rape them for hours (or even years), and then kill them or sell them into slavery. All of these are different crimes and all deserve appropriate penalties.
