Are the pepper seedlings indoors or outside? This type of seed needs heat most preferably from the soil or what we call bottom heat to jump start the seedlings. Unless you live in a very warm region heat lovers like tomatoes or peppers should be started later in the spring just 4 to 6 weeks before the last frost date.  You can try covering the seedlings with protection at night as even night temperatures below 50 degrees could stunt the growth of peppers.  May is not too late to try planting a fresh batch of seeds for pepper harvest this summer. Full sun and warm nights will get your peppers growing fast. Keep growing, Marianne Binetti