To give you some guidance this is what I say:
3-4 months – after newborn this is the next stage to capture lovely images, beaming gummy smiles a plenty!
7-8 months – when baby is sitting comfortably, is happy being on their front and has discovered their toes…. 🙂
1 year – Nothing better than some gorgeous portraits followed by a cake smash session!
Hope that helps 🙂