Here you go, write your heart out, it won't be the statistics you were hoping for but they weren't that hard to find:

The majority (77.6%) of perpetrators were a parent of a victim, 6.2 % of perpetrators were a relative other than a parent, and 4.1% had a multiple relationship to either multiple victims in the same report or multiple victims across reports . Nearly 4.0% (3.8%) of perpetrators had a "other" relationship to their victims. According to states' commentary the NCANDS category of "other" perpetrators relationships include foster siblings, nonrelative, household staff, clergy, etc., Please refer to appendix D for more information. (see table 5-5 and related notes)

According to other data in the report 2.36 per 1,00,000 kids die from abuse/neglect on a national average, that's 1,750 kids in 2016, of those 1,750 kids 85 died while in the system.

That's about as much time as I am going to spend on it, now if the stats came out that more kids really did die in foster care then by abuse of their own parents this site would rave and up vote me like mad...but since it doesn't it's a waste of my time. One is to many kids dying, there's stats in their that will tell you how many kids also died after being returned to their parents, it's all heartbreaking but with well over four hundred thousand kids in foster care the system is not always going to be perfect, there are five states who have been or are being investigated because there are to many deaths in the system in those states, but they would also include deaths where CPS hadn't removed children and were monitoring parents or gave children back and those parents were being monitored or let out of the system...there's so many variables but this site isn't worth it to me to search it all out and lay it out, they probably wouldn't like the results anyway.
https://www.acf.hhs.gov/cb/resource/child-maltreatment-2016