my seedlings are about 8-9 days old..under a 400 w hps..the thing is I had ants in there,and they killed 4 of them..the rest that survived,had their cotyledons completely eaten off,and half of there first set of serrated leaves..now I placed them in a tub of water to drown the ants..so will getting their cotyledons and half of the leaves eaten stunt them..or will they just keep on growing there next set of leaves like normal?
Once you get that first set of leaves after the cotyledons the cotyledons generally die off anyway so losing those shouldn't make a big difference. You may experience a temporary stunting or slow down of growth simply because the plant has less leaf to draw in energy from the light. Once it can put out some more leaves though it should continue to grow like normal, provided the ants are gone. You may want to try something like the No Pest Stripe made by hotshot. I don't know if they work for ants but I know they work for things like fungus gnats and other insect pests. They only cost a few dollars and generally provide 3 months of protection.