Welcome to OG!
They just look hungry. Specifically it looks like a potassium deficiency but nothing to worry about. If you're feeding regularly you might consider increasing your dosage. They look like they're switching to flower right now so they're searching for more P and K.
Your seedlings look great! The minor curling on the edges is natural and is caused by transpiration, usually from too low or too high RH values. They'll adjust if you don't
Will be following along!