How can this sentence be changed into passive voice:
"My mother let me play today."
which one is correct:
- I was let to play today by my mother.
- I was let play today by my mother.
The technically correct answer is
I was let to play by my mother
but let is not usually used this way and will sound awkward. It sounds so awkward that you should consider it incorrect to use.
A native speaker will probably think you're trying to say I was left to play by my mother.
You should say I was allowed to play by my mother instead.
Let out doesn't have this problem, though. But the meaning is slightly different.
The dog was let out by someone.
"My mother let me play today".
There is no passive here given as "was let". The verb allow must be used to give a passive meaning. let means allow. Please note: My mother allowed me to play today.
"I was allowed to play by my mother today".
The only passive use is when let means let out or rent, as is:
Who let the dogs out? [like the song]
The dogs were let out by me.
Who let (out) this apartment?
This apartment was let out by an agent.