However, it is suggested by the cabin crew even that one should fasten their seat belt when seated in case of unexpected turbulence.

Yes, accidents do happen.. and suddenly too. Then who is to blame if baby goes flying onto the ceiling?

You do have the right to demand that the baby be placed with the mother so that you shouldn't have the responsibility of baby-sitting.

The CX FAs too display a lack of authority here. They should insist that the mother take responsibility for her actions, like maybe let her sign a waiver absolving all fault should the aircraft hit severe turbulence.