My first thought would be too wet and not enough aeration in the soil mix.

Do you have them in 50% sunlight. They should not be in full sun all day until they have 3 or 4 true leaves.

Rick

Rick, Thanks for the reply. They have 2 to 3 hours of sunlight. I water everyday so maybe I overwatered.

Germination until two leaves - water constantly

After two leaves - cut back watering drastically

If soil does not drain and have adequate aeration. Constant watering is definitely not good no matter what age of seedlings.

Rick

too damped, will cause root rot on seedlings, you can water them all you want as long they get full sunlight and not just 3hrs, if they were born outside can withstand full sunlight but if grown inside, around half day of sunlight is fine, adeniums are tough seedlings against sunlight