The pediatric profiles are derived from the vitals profile. which lists all the elements as "must-supoprt" the spreadsheet generated profile do not inherit this (probably since cell was left blank) resulting in a must-support = false. nor did the validator catch this
as noted on this Zulip chat: https://chat.fhir.org/#narrow/stream/179252-IG-creation/topic/must.20support.20error.20not.20caught.20by.20validator

Technical corrrection is to update the SD to make all the inherited element must-support= true.

see http://build.fhir.org/profiling.html#mustsupport

"If creating a profile based on another profile, Must Support can be changed from false to true, but cannot be changed from true to false. Note that an element that has the property IsModifier is not necessarily a "key" element (e.g. one of the important elements to make use of the resource), nor is it automatically mustSupport - however both of these things are more likely to be true for IsModifier elements than for other elements."