Which Son Should He Choose?

A man once had a small succah and he could only fit one of his two sons in the succah together with himself. One of his sons was bar-mitzva while the other was at the age where the father had to teach him to do the mitzva of succah [גיל חינוך].

At first blush the answer is simple - the older son is obligated from the Torah while the younger son is only obligated Rabbinically so of course the older son should be given preference.

Not so fast. Rav Eliayashiv paskened that the YOUNGER son should be given preference. His reasoning was that the obligation of the younger son devolves upon the father [according to Rashi Brachos 48] while the obligation of the older son is ihs own personal obligation that has nothing to do with the father. All the father has is a general obligation of ערבות - all Jews are responsible for each other. The father's personal obligation supercedes his general obligation of ערבות [albeit מדאורייתא] so he should allow his younger son in the succah.  

Others argue with this psak. If I were on a deserted island and asked this question and would not know that Rav Eliyashiv said otherwise I'd go with the older son....

עיין קובץ קול התורה מג עמ' קנב