can be seen as a sight that：~の兆候と見られる

息子が縮み上がる言葉を見つけた。
"鬼が来るよ。"
私がそれを言うと、いつも彼は恐れ、私に従う。
これは彼の想像力が成長している兆候だろう。

もちろん頻繁には言わないが、
自分がってな態度を取られてどう扱うか難しいときに、仕方なく言うのだ。

でもいつか効き目がなくなることは確かだろう。

I found words which made my son cringed.
“ Devil would come.”
When I say it, he always gets scared and follows me.
It can be seen as a sign that his imagination skills have been developed.

Of course, I don’t say that so often.
When I face the difficulty in dealing with my son’s selfish behavior,
I reluctantly say that.

But I'm sure that it won't work someday.