DS has just turned 1 and is usually very well behaved. He's been drinking juice from a Tommee Tippee beaker for a while with no problem. Just lately, every time he takes a sip he then lets it all dribble back out of his mouth. I've tried telling him off and taking it off him every time he does it but it hasn't made any difference.
Does anyone have any ideas why he's doing this and how to stop him? Apart from it being an unpleasant habit, he's also not drinking anything because it all comes back out again.