There are a few strategies you can try to help your child keep track of their things:
Encourage them to make a checklist of items they need to bring with them each day, and have them check it before leaving home or school.
Assign a specific place for them to put their belongings when they come home, such as a designated hook for their backpack or a designated drawer for their clothes.
Help them label their belongings with their name or initials.
Create a reward system for when your child successfully keeps track of their things for a certain period of time.
Lastly, it could be helpful to have an open conversation with your child to understand why they might be losing their things. It could be a sign that they are feeling overwhelmed or stressed and extra support is needed.