Bender was made in an assembly line and was fed alcohol. Why was his kid drinking milk?
If anything, baby robots should be fed a diet of metal, silicon, and plastic. The building blocks of life!
Milk contains a sugar that can be polymerised to form a bioplastic similar to cellulose (which is what sellotape, wood, paper, and some plastic drink bottles are made of), and other chemical units that can be processed and polymerised to form a biodegradable thermoplastic suitable for use as a film or membrane. Both of these would be very useful polymers for a young, growing robot.
Pretty much anything with organic chains in it is a useful feedstock for robots in the Futuramaverse. Alcohol provides energy, but they also ingest oil and other substances. The beer with metal shavings in it from TROAE, for example. The stuff that Bender orders when dining at Elzar's. There's no reason that I can see why a robot wouldn't see milk as a potentially useful dietary intake of raw materials.
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