When referencing a model’s child relationships (e.g., in template merge syntax), what is the difference between {{myChildObject__r.records.length}} and {{myChildObject__r.totalSize}}?

Without any record limit or conditions on the child relationship, I assumed records.length would give the total number of child records for a given parent, but noticed a discrepancy when viewing a parent record with over 200 child records. The latter (totalSize) is giving me the correct number, whereas records.length shows 4.  This was also the case when looking at the model’s properties in the console.  Again, I have not set any record limit or conditions on the child relationship.

This is on version 11.2.1 – not sure if this is relevant to later versions, but I can’t update this org just yet.

Thanks!