Not sure how to say these...

[Simba]

From Genki chapter 4:

"I often ate hamburgers when I was a child."

My attempt: わたしはよくこどもにハンバーガーをたべました。

And: "Takeshi did not study much when he was in high school."

たけしさんはあまりこうこうにべんきょうしませんでし た。

I don't think either are *quite* right but I'm not sure quite how to fix them.

Help please ?

~~Simba

[Nathan]

私（わたし）は子供時（こどもとき）によくハンバーガ ーを食べました（たべました）。

I, during my childhood, often ate hamburgers

たけしさんは高校時（こうこうとき）にあまり勉強しま せんでした　（べんきょうしませんでした）。

Takeshi, during his high school days, rarely studied.

Perchance.

[Simba]

Thanks very much, that 'toki' word is useful!

[karatakid]

I just see little squares

[Cyclamen]

私（わたし）は子供時（こどもとき）によくハンバーガ ーを食べました（たべました）。

たけしさんは高校時（こうこうとき）にあまり勉強しま せんでした　（べんきょうしませんでした）。

Gramatically speaking, it would be correct to put a の between a noun and 時. Those sentences would be then 子供の時 and 高校の時.
I'm not sure if the の*could* be omitted in spoken japanese, but from what I heard, it's always used.

[Simba]

Thanks very much, Cyclamen .