My son, who hit 1 year Saturday, will only drink from my breast or from a bottle. I'm having a really hard time getting him to try trainer cups. He can hold them just fine but refuses to drink from them, no matter how much we market it, no matter how hungry/thirsty he is. I've tried putting all kinds of things in there--diluted grape juice, breast milk, formula (which he also consumes). I admit he ends up getting so upset I end up either nursing him or giving him a bottle, so now it's feeling a lot like a power struggle. I've even tried making sure he's had enough to not need liquid urgently before encouraging him to finish things up using a cup. Any advice/suggestions?