You need to move them to larger pots asap. It also looks like you may be overwatering. It is very hard to water correctly in those type of seedling pots. Put them into solos. What type of soil are you using? Looks like it may have time release fertilizer, which is released as you water. This can cause nute burn and lead to stunting and other problems. Mix some more perlite into your soil. It will drain faster and alleviate some of the problem. Whatever you do, don't give them any more nutes if the soil has fertilizer in it already.