The salvation through a child has a possible reading as fulfilled history if that child is associated with Hezekiah. However, the titles and imagery surrounding that child do not appear to fit a temporal or present fulfillment of the verse. Unlike the possible misappropriation of a limited prophecy into a Messianic one that we saw with the child Immanuel (2 Nephi 17: Isaiah 7) this prophecy occurs in the context of purposefully dual prophetic/poetic language. This verse certainly may be read with a future reading, and references to the Messiah are unmistakable.
Nevertheless, the verse is not without its problematic reading. Irvine provides a translation and comment for this passage:
"Isaiah 9:5 For a child has been born or us, a son has been appointed for us. And authority has fallen upon his shoulder and he has been named Wonderful Counselor, Mighty God, Everlasting Father, Prince of Peace.
This translation highlights Isaiah's conspicuous return to the past tense. The Hebrew verbs are either perfect forms or imperfect consecutives. The verse, then, does not predict a future "child" but reflects on a past event and its significance for the present.
.. Many scholars defend a future messianic interpretation but this understanding must be ruled out, if the verbs genuinely refer to a past event." (Irvine, 1990, p. 229.)
Of course, Irvine's analysis depends upon reading the past tense as historical, rather than a future guarantee. It is not unknown in the prophetic nature of the Lord to view a future event as through it had already happened. Indeed, the combination of such past/future expectations is interestingly combined in a different translation of this passage:
"The prophet saith to the house of David. A child has been born to us, a son has been given to us: and he has taken the law upon himself to keep it. and his name has been called from of old, Wonderful Counselor, Mighty God. he who lives for ever, the Anointed one (or messiah), in whose days peace shall increase upon us. (The Targum of Isaiah. tr. J.F Stenning. Oxford at the Clarendon Press 1949, p.32.)
In this translation we have the retention of the Hebrew's past tense, combined with the explicit delineation of the Messiah as the one who fulfills the promise. I suggest that such a reading is not possible without the ability to see the past tense here as a representative of an assured future. This is a prophecy, and one that is emphatically to be realized.