It finally took a parent watching a 3 year old play with the 6 month old sibling at home and actually biting on toes and fingers and tummy and leaving teeth marks and when asked what are you doing claimed she was playing with baby just like daddy does. Lightbulb moment. Play routines changed at home and problem solved at daycare - keep your mouth to yourself. Child was made to kiss her hand and plant the kiss for the next while till she proved she could kiss safely. At daycare it was hugs only for sibling who was coming into care at 10 months.