I can't see any spots pal.
Have a good scan around though and look for mites. As little white dots are usually associated with them. As your plants are young. You can quickly fix this. Either get some AMC spidermite wash. Or a 50-50 h202/water will help kill any off.
They are really young, so it wouldn't be mold or anything.
Also if you are spraying your plants with anything it could be just that drying in? (Try rub it off, If you haven't already, Ph Adjusters will leave a white substance on your plants when it dries in or if you've used anything else
Good luck.