English Translation
Perhaps it is only in childhood that books have any deep influence on our lives.
Unnatural word-for-word translation… We don’t usually translate “we” in English to 我々（われわれ）. It sounds very wordy and unsophisticated.
Also, ～に対して is wordy.
My alternative translation is:
書物が人生に強く影響を及ぼすのは、おそらく子供時代だけだろう。
The adverb “perhaps”/おそらく should be put closer to 子供時代 for a better collocation although the original word order is understandable.