RRSPs used to get reported on a different form. The year that form was discontinued, the IRS instructed us to report is as an "Other Foreign Asset". So I continue to report it that way (even though Custodial Account seems to make the most sense). Have a look at page 1 of the 2014 instructions for Form 8938:
https://www.irs.gov/pub/irs-prior/i8938--2014.pdf
