You can use Strongid. It’s both useful for the foal but also for the mare. In generally the dewormers are the same that adults, but just the quantity changes. If it is a young foal, you can make a year of transition by including the Distri'Vern (it’s a specific dewormer) in the deworming protocol this will treat it in a less aggressive way for the intestinal flora.
Have a good day :)