I always say that we can only start from where we are. That's just logical. God forbid that I should start again, but I would start with Love and remain with Love in its myriad manifestations.
One cool thing is to chant softly to the child. Do Aum, the mother of all mantras. Soft short A and a gradually long UM. Repeat a few times. Sound and silence will be very useful to the child. Sing, play music. Hug to encourage bonding, but not too much. It can spoil them when they grow up.
If you are home for at least two years post birth, or the mother is there, then that's awesome, but one year is great too. My view is that six months is too short.
What you do will be very practical: make the child laugh; make faces, jingle bells, make childlike playful sounds ... you're asking about giving advice but they can't talk or understand the human ways at this stage. Use their way. I would ask the parents not to shake or allow others to. A gentle bit of play is cool, but no hard stuff. Krishna's blessings bro. You got one?
Note: God is always first followed by parents, but this does not mean anything esoteric or a man in the sky. From as early as 18 months you can start teaching them to relate to the sweet feeling inside them; read loving books. Hindu bookshops are full of sweet and charming children stories with pictures.
There is a very small pictoral book sold by Hay House on the net. It's called, I Am, by DR Wayne Dyer. So beautifully written for kids!