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Why would Abraham put a 14+ years old boy on Hagar's shoulder?

Comparing the age of Abraham when Ishmael was born (86 years old. Genesis.16:16) with his age when Isaac was born (100 yrs old. Genesis.21:5) Ishmael was at least 14 years old when God persuaded Abraham to send them away. ... See More

The AV reads:
"... Abraham rose up early in the morning, and took bread, and a bottle of water, and gave it unto Hagar, putting it on her shoulder, and the child, and sent her away ..." (Genesis.21:14)

Reading this many understandably visualise Abraham strapping a teenage boy to his mother's shoulder for her to carry him. Is this what the Hebrew text is saying? Critics see this as a fault in the scriptures. So we need to examine it carefully.

According to John R.Kohlenberger's Interlinear of the OT the sequence of the words of Genesis 21:14 in Hebrew is:

and he rose Abraham in the morning and he took food and skin of waters and he gave to Hagar setting on her shoulder and the boy then sent her off

Each underlined grouping of words represents one Hebrew word.

Brother Fred Miller has drawn my attention to his extensive notes on Hebrew idiom in his commentary on Isaiah.48:16 from which I gather that, in Hebrew syntax, when there are two subjects to a verb and one is dominant, the dominant one takes a singular verb and the "also ran" subject is tacked-on after. For example in Genesis.3:8 the Hebrew word order is "and Adam hid himself, and his wife". This does not mean "Adam hid his wife ..." but it means "Adam and his wife hid ..." Adam taking the leading role. Similarly, when a verb has two objects, one more dominant than the other, the lesser is tacked-on as an "also ran". For example in Genesis 1:16, where, according to the Hebrew word order, God made "the lesser light [i.e. the moon] to rule the night and the stars", it is saying that God made the moon so as to play the leading role in ruling the night and made the stars to have a lesser role in ruling the night. For this reason both moon and stars are subjects of the infinitive "to rule". The best way we could express that in English might be to use parenthesis and translate it as: God made "the moon (and the stars) to rule the night." [Hebrew scholar Fred Miller's commentary on Isaiah can be seen on the WEB at :-
http://www.ao.net/~fmoeller/isaiahdi.htm].

Similarly "and he rose Abraham in the morning and he took food and skin of waters and he gave to Hagar setting on her shoulder and the boy then sent her off" is telling us that Abraham took food and water. The food and water are then, dominant in thought, and so become the direct object of the verb "setting" in "setting on her shoulder" and also the primary object of the verb "gave" in the clause "and he gave to Hagar", The noun "the boy" is in the accusative case and is the less dominant direct object of the verb "gave". So it is tagged on after the clause - "and he gave to Hagar setting on her shoulder". So according to Hebrew syntax there is no grammatical connection between the noun "the boy" and the present participle "setting ". Ishmael is not put on Hagar's shoulder. Ishmael is given to Hagar.

Maybe the most succinct way of putting it in English would be to use parentheses here as well, and to render it: "... Abraham arose in the morning, took food and a skin of water, gave it (and the boy) to Hagar setting it on her shoulder and then sent her away "

It makes sense for Abraham to be seen to give Hagar provisions for her departure and also (in the light of the culture of the time, where the son was the property of the father and the child's mother could not take him unless the father gave him to her) for Abraham to be seen to give Ishmael to her, thus relinquishing his claim on the boy and placing him in her charge. This is expressed so succinctly in the Hebrew but it is difficult to convey it in English.
هل يستطيع احد ان يترجمه لي باختصار