So last saturday I was out with my partner, his two children from a previous relationship and our baby that we had together. We was on a walk and baby started getting a bit stressy. So I got him out the pram and was carrying him. My partners daughter who is 9 was talking to him and then she slapped the baby on the head! For no reason. I told her off and she just grinned at me. My partner didn't say a word? Said that I'd told her off that there was no point him saying anything? She didn't apologise and just carried on like normal. Baby is only 14 weeks. She does behave badly most the time a few weeks ago she spat at her older brother. But I don't really want her around the baby now? I don't know what to do?