Do some of his behaviors seem regressive?
Is she clingy and doesn't want to be separated from you?
Has he told you he wants to stay at preschool and not go to kindergarten?
Are all of these behaviors not typical for your daughter?
When I was a pre-K teacher I would hear these concerns from parents every year around the end of January or early February. The parents would understandably be very concerned and ask me for advice. As a child therapist I still hear parents express these same concerns about their five year old.
I validate the parents concerns and then I ask if they're recently registered their five year old for kindergarten? The answer is usually "Yes!"
I then proceed to explain to parents that this is a big transition for their five year old. Everyone is telling them how grown up they are and talking non-stop about how great it will be to go to kindergarten. The child feels torn. They're excited to be growing up but they're also apprehensive about leaving preschool and all the familiarities they're grown accustomed to.
It's a big step for a five year old and as parents you can help them with that transition. If you see the above mentioned behaviors take a few minutes to give your child an extra hug and ask them if they're feeling sad or scared about leaving preschool and going to kindergarten. Validate whatever they are feeling and offer helpful suggestions such as driving by the new school and taking a photo of them standing in front of it. Mark on the calendar the day your child will be going to the school for a visit and/or kindergarten screening. Make sure that during that visit you point out the bathroom because not knowing where the bathroom is located is a big concern for a soon to be kindergartner.
Put less emphasis on growing up and more on making the transition easier for them.