Like some responders already said, being able to hold it all night is something you just have to wait for them to develop physically.
My oldest daughter was potty trained day and night the month she turned two. My husband put panties on her and she never looked back! My second daughter wasn't dry consistently at night until she was 4 1/2 years old! I was really tired of spending so much money on pull ups! Right now my third is potty training during the day, but I've noticed that after a nap or when she wakes up, if I catch her right away, she'll be dry and go on the toilet for me. But if I am just a minute late, then she's wet.
My sister's son was 8 before he quit wetting at night, and she tried everything I'd ever heard of and many things I hadn't! His doctor said the same thing - some kids just physically can't do it until they're much older than others.
Blessings!