Throughout history is a long time and covers all continents. To be able to know the average of how many, say, lived to adulthood or actually got to rule, that would require someone to gather up all the information from thousands of years of African history, Asian history, Europe, the Americas and Australia continent history. On some perhaps a database could be made of what is known to give a sense of how lived and got a chance to rule, who got killed before they had a chance (though that isn't always clear), who simply died off. I am unaware of any such project that would give the numbers to go "well most lived to reign/died young/got killed" or not.

In terms of success, that would be beyond any realistic reach of such a project. Glancing at a history is not going to gain the compiler knowledge of politics at the time, the trustworthiness of the sources, what was might have been a realistic measure of success given the challenges and what failures might want to come with an asterisk. Or why that ruler was successful or why things crumbled, how much that might reflect the childhood or other things.

If I might suggest, the question is too broad and impossible for people to answer, nobody here is an expert on all the history in the world so can't answer. The challenges and threats facing child rulers, how it might have an impact on their rule, is an interesting subject but it might be best to find a question that is narrower in focus where people can speak of those in their era rather then seeking an answer for all of history.