soil looks a bit dry. do you have a hood to cover it? if not cut a coke bottle in half, spray the inside with water and pop it back on. spray it every 4 or 5 hours.
sorry just re-read your post. those first leaves are called cotylidons(thats not the right spelling but fuck it), there not 'true leaves'. they do fall off anyway, yours do seem a bit earlier than usual. do what i suggested though, its the best way to bring on seedlings, they love humidity. dont worry about those leaves.