Translation of "детски" in English

Она говорила по-детски.

She talked childishly.

Это очень по-детски.

That's very childish.

Когда я говорю на японском, это звучит по-детски.

When I speak Japanese, I sound like a child.

Том сказал Мэри, что по его мнению, она ведёт себя по-детски.

- Tom told Mary he thought she was behaving like a child.
- Tom told Mary that he thought that she was behaving like a child.
- Tom told Mary he thought that she was behaving like a child.
- Tom told Mary that he thought she was behaving like a child.

- Почему Том так по-детски себя ведёт?
- Почему Том ведёт себя так по-ребячьи?

Why's Tom behaving so childish?