DD has just turned 9 months and has only been sitting unaided for 2 weeks. She's not really showing any interest in climbing, crawling or pulling herself up. She's quite happy just sitting with her toys around her or flying around in the baby walker. She's also not mastered a sippy cup yet, just throws it around but doesn't drink.
She's weaning well though, eats most food I offer her and has a good appetite. She's alert, babbles a lot, laughs and engages well with her toddler brother but just seems so behind where he was at the same age. He was crawling and pulling himself up and drinking from a cup; she still feels like such a baby. Should I be worried? HV said only to get in touch if she wasn't sitting by 9 months but she was so close to that age when she did.