I forgot that rape was till the point of ejaculation.
It's not ... that was a particular case here. However, in many states rape requires penal penetration which requires an erection.
As defined in the Puerto Rico statutes it appears that there is no crime of "rape" as all forms of sexual assault are covered under the single category of "sexual assault" since 2004.
The point is that the term, "rape" has a specific LEGAL Definition within a jurisdiction and its use is often legally inaccurate. For instance, in my state consensual sexual relations between an adult and a minor is not "statutory
rape" it is generally titled "unlawful sexual intercourse" because here, "rape" means something else entirely.
I am often suspicious when the term is used because it most often implies a forced sexual assault. When someone is alleging that a 10 year old boy forcibly sexually assaulted an 11 year old girl, I am going to be suspicious because statistics and experience tells me this is highly unlikely. And since we are getting that information from a third party whose son is charged with a related offense even though he allegedly only witnessed it, it only confirms my suspicion that there is information missing. My guess is that the 13 year old is being charged as an accomplice in some way, and I further suspect that "rape" may not have occurred, though perhaps some form of sexual assault did. Maybe, it was a mutual "look what I have in my pants" situation where the parents found out and called the cops. We don't know.
There are unanswered questions here, and we will never KNOW the answer because the OP is not apparently privy to the answers. What is notoriously missing is under what theory the OP's son is being charged if all he did was see the offense.