Hi,
I've been thinking about this and a baby who is named as a dependent on, say the 175 Skilled Independent visa application, will have to have it's own passport - see form 1276 Part F question 57.
Any dependent will have to have their own passport because they will have to have their own visa stamp - bit silly if you've got a 3 month old baby and you don't move over for a year....their photo will look nothing like them...but them's the rules
Dolly
PS hopefully an agent can clarify