Anxiety and fear are worries about what may happen in the future, so bringing the mind back to the present is a good way to develop resilience. Mindfulness is simply paying attention, and the best way to pay attention is by using your breath. Mindful meditation helps to manage stress, increase self-control, and sustain attention.
Plan to have mindfulness breaks on a daily basis (15 minutes right after nutrition break can work really well). Take mini-breathing or meditation breaks throughout the day to bring the mind back to the present. For some children, adding in an active component (mindful walking or yoga) can help with restlessness. There are a lot of excellent resources online as well as pre-recorded guided meditations to use. Find one that is age-appropriate and works well for your child(ren).
Here’s a recommended guided meditation for young children who are new to mindfulness from Shambhala called “Sitting Still Like a Frog”. https://www.shambhala.com/activities-download-sitting-still-activity-book/