Boy toddler of 25 months loves his baby sister of 8 months but has just started a phase of grabbing at her face (she looks like she's been in a fight)! He doesn't seem bothered then just grabs randomly! Plenty of other times he could do it and doesn't, just plays nice nearby or with her. This behaviour doesn't seem to have a pattern such as when I have done or said something. It's quite hard not to react by shouting, although I'm sure that's not the answer. Any tips?