It's the end of January, and many of this years foals may be reaching 3-4 months old now (as is my colt, pictured) so it is about time for their first deworming. It is wise to get a FEC done beforehand however, to confirm strongyle infection (egg in top photo; 95% of all worm infections) or if Parascaris equroum, a.k.a. Ascarids, a.k.a large roundworm (egg in bottom photo) is present as well.
Strongyle-only infections can be treated with any wormer, although at this time of year I would lean towards an avermectin, while P. equorum should be treated with a BZ wormer to limit the chances of blockages of dead worms.
P. equroum positive foals should also be monitored more closely for re-infection, with FECs every 8-12 weeks, as these large roundworms can cause serious illness in young horses.
Foals with strongyle-only infections can be treated at between 3-5 months old and then again at weaning in late autumn/early winter to also catch any bot flies as well. Then a third FEC/deworming should be done in early spring, and then as a yearling they can go onto a regular 3-4 FECs a year until they reach maturity.
If you'd like to organise a FEC for your younglings, check out the website for drop off points/dates and the submission form for postal samples.