JRPass

Children ticket

Hello,
I have a vacation trip in Japan during 20-27 april 2012,using the JR pass.
We have 2 adults and 2 kids, aged 9 and 5++.
My younger kid is 5 yrs and 11 months during the trip (his 6 yrs old birthday will be on 28 april 2012,just after we leave Japan!) The question is - Can we buy 2 JR tickets for adults, one ticket for the older kid
and free pass for the younger kid? (we accept that it may have no seat for him on some trains) Thanks, bests for you
Praj :-)