mx.psbkids.com has no NS records.
NS records for this zone are defined at psbkids.com.
NS records for this zone are defined at psbkids.com.
Question and response
Question
dig mx.psbkids.com. NS
Answer
The response has no answer records.
Authority
psbkids.com. 3600 SOA dns.psbkids.com. hostmaster.psbkids.com. 1173805803 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0