I live in the UK on a Tier 2 visa, and my son was born in the UK. According to https://www.gov.uk/tier-2-general/family-members:
If you have children while you’re in the UK, you can apply for permission for them to stay.
You must do this if you want to travel in and out of the UK with your child.
When you apply you must send a full UK birth certificate showing the names of both of your child’s parents.
Is this permission to stay the same as a Tier 2 visa? Also, where do I apply for this permission and where do I send the birth certificate to?