HI Dayanara, thanks for using Ask Extension.

Actually, these seedlings look good. The leaf curling and slight stem bending you’re seeing are common physiological responses in young tomatoes and are not caused by insects or disease. The growing tips look healthy and are producing normal new leaves. Young tomato leaves can curl slightly as they expand. Moisture fluctuations may cause a temporary drooping.  The plants could be stretching for light which can look like curling. Limited root space can cause plants to respond with thinner, more stretched stems. Warm indoor temps can sometimes cause a stress response.   You could check out the roots to assure they are not crowded. Make sure the plants are not reaching for light.  Water to keep the soil moist not wet.  Nutrients may be required but don't overdo it, some potting soils have added nutrients.  With the cold temps in the near future, it would be good to wait planting outside until nighttime temperatures are consistently above 45°F and the soil is warm. Check out the following link:

Tomato growing guide | Cornell Garden-Based Learning

I hope this is helpful.