According to the FBI, in 2019 there were 421,394 NCIC entries for missing children. In 2018, the total number of missing children entries into NCIC was 424,066.
This number represents reports of missing children. That means if a child runs away multiple times in a year, each instance would be entered into NCIC separately and counted in the yearly total. Likewise, if an entry is withdrawn and amended or updated, that would also be reflected in the total.
You also have to consider how the cases are distributed. The vast majority are runaways, not abductions:
In 2019, the National Center for Missing & Exploited Children assisted enforcement and families with more than 29,000 cases of missing children:
91% endangered runaways (of the nearly 26,300 runaways reported to NCMEC in 2019, 1 in 6 were likely victims of child sex trafficking)
4% family abductions.
4% critically missing young adults, ages 18 to 20.
estimated 150k child sex slaves in the US. 10k children disappear each year from foster care. 3 of 4 children in foster care are sexually abused while in the system.
The information is out there:
https://www.missingkids.org/footer/media/KeyFacts
You also have to consider how the cases are distributed. The vast majority are runaways, not abductions:
In 2019, the National Center for Missing & Exploited Children assisted enforcement and families with more than 29,000 cases of missing children:
estimated 150k child sex slaves in the US. 10k children disappear each year from foster care. 3 of 4 children in foster care are sexually abused while in the system.