Sup! So there are two things I think it could be and several ways to figure it out and treat it. Firstly, inspect your plant with a magnifying glass or jewlers loupe and see if you notice anything crawling around. Make sure to check underneath the leaves and the soil. If you find some bugs, try and identify them or photograph them, post it here and we can figure it out.
Second, check the PH of your nutrient solution. You want it around 5.9-6.1 for coco. If it's not 5.9-6.1, then adjust it accordinlgy with a couple drops of either ph-up or ph-down.
Third, check the ppm/ec of your nutrient solution. As babies you dont need more than 1,000 ppm as long as you dont use CO2. However, you dont wanna go below 600ppm as you will start to have deficincies as they get bigger. So, adjust your nutrient ppm's accordingly if you notice they are out of range.
Lastly, it might come down to tempurature, humidity and/or your light levels. You want it around 70-77 degree's in there and 60-70% humidity for vegging plants.
Your lights should be around 30DLI at this point, slowly increasing to 40DLI until your ready to flip, but sometimes this intense light is too much, so turning down the light will help it be less stressed sometimes. Dont know how to read the DLI? No prob, just download the Photone app on your phone and it does a damn good job of measuring your light intensity. Dont go by PAR because it is only PART of the total info needed to calculate the amount of light your plants are getting, go by DLI.
Anyway happy growing, feel free to ask as many questions as you'd like. We got you!