Here is an update on what I've discovered.
I have received Frederick William Burnard's birth certificate from the GRO. As suspected, his father's name is absent. Perhaps the Foundling Hospital Petition for Admission will contain his birth father's name; unfortunately, this document will not be available until the digitization is completed in 2024.
I have discovered that the Lewis Cox family at 59 Aldenham, where Amy lived and worked when she gave birth to Frederick William Burnard in 1897, has another connection to the Burnard family. Amy's younger brother, Frederick Charles Burnard, married Lewis Cox's daughter, Lily Cox, in 1899. Frederick and Lily then moved to 59 Aldenham with their young family a few years later and appeared to reside there for many years.
I am still curious to know where Amy raised Frederick William Burnard over the course of 10 months before she placed him with the Foundling Hospital (is it likely she would have remained at 59 Aldenham to work and raise her child?) I am also curious to know how Amy came to work for Abraham Drapnik, in a different part of London, by 1901. Both questions very difficult to answer!
Finally, I am still hoping someone who regularly visits the LMA can have a look at the registers noted at the beginning of this post to see if there is a page in the Foundling Hospital General Register with information for Herbert Day and, less likely, a page in the Apprenticeship Register (Herbert did not apprentice, but instead emigrated to Canada, so he may not be listed here).
Thanks again everyone