Sounds like the weather is agreeing. Still, I would be prepared to blanket if the foal appears to be cold (excessive shivering).
Also, keep them out of the direct, hot sun for at least a couple days til the hair grows back some to protect the skin, esp. if it's pink.
Don't clip with more than a #10 (ten is usually the longest clip though I have some that are 7s and I know there are lower numbers) for a foal and first clip. Have your foal as clean as possible (vacuum/blow or bathe, first). Apply some showsheen as they dry to help w/the clipping (for the nicest job possible).
I don't have Wahls anymore, but I would guess they have a #10 blade?
That should be all you need. Clean the blades every few minutes (blowing w/compressed air, brushing them out is good) and relubricate with blade oil before starting again after wiping the excess oil off.
If you feel cold outside wearing a t shirt and shorts, then it is likely you should put a blanket on the foal, and if you can't stall them at night (don't know what the temps are like there), I would maybe do a modified clip as in clip head/neck/legs and underbelly for heat relief, but leave a "blanket" of hair for some warmth protection.
I have clipped them as young as two or three weeks, but usually only a bit at a time at that age. Mine usually get their first clip job by the time they are two months old.
Liz M.