I would use the age difference as a defence. Please remind child XXX and I will remind her too here at daycare that she is 4 years old and that there special toys for the grown up children to use that the younger children either are not allowed to use or show little interest in. It is also important that the older children realize this and allow the younger ones to have first access to some of the baby toys.
Since child XXX will be starting school soon, it is important that we remind her that now she is 4 and that with that comes expectations for learning, playing and behaviour. She will have a much better experience both in daycare and at school if we can help her with this.