Dependant child - third party consent letter; how to put the baby's signature

Hello all,
I am a prospective student in the UK (I have obtained a student visa already). I am applying for the visa of my child (10 months old). His application requires a third party consent letter that needs to be signed by the baby himself. This completed application form should be uploaded online prior to the visa interview.

How can I do that? Should I put his fingerprint? Or can I sign it on his behalf?

Hi,
You can sign on behalf of the baby, please ensure you indicate that you're the child's mother below the signature.
Just a simple: (Mother of "Baby's name") below your signature should do.