Sounds like they are rather small still... The mix you have them in now is probably all that is needed. I'm no expert or anything, just my thoughts. If you do fertilize, I'd do it at about 1/4 strength - around once a week. I do my seedlings at 1/4-1/3 strength MG once a week - but mine are in the most dirt cheap potting soil money can by, absolutely no nutrients in there!

Yeah, 1/4-1/3 strength fertilizer is generally a good idea.

I usually wait until the 1st set of leaves are leafing out well (not counting the cotyledon/feeder leaves that emerge first and generally drop off) and the 2nd set is showing before I fertilize unless there's early visual signs of nutrient stress.

Rarely do I have to fertilize before that point. It all happens rather quickly after the 1st set of true leaves emerge.

Exactly what these guys mentioned.
Once the seedling has the first set of True leaves, you can start fertilizing at 1/4 strength (to be on the safe side). Use your discretion, and work up from there.

Josh

Thanks all, some are on their third sets of leaves popping out and that set looks a little yellow that's why I ask. Also how the heck are aphids finding their way into my garage. I have no other plants but my seedling peppers and tomatoes. The potting mix was all new purchased items. Is it to early to spray them with something.
Thanks again,
Rey

Probably Kellog's garden soil and worm castings had needed nutrients to get them going up until now. So I think nc-crn and Josh made the right recommendations. I do the same thing.

Aphids find a way....

And yes, you can spray/treat your seedlings. I use Neem oil at the first sign of trouble, and I'm sure to smash any aphids that I see.

Josh