Actually there is quota system in IR.So different stations have different quota.if that is exhausted,then people get W/L.
Now in ur case i donot have any idea whether that RQWL will get confirm or not.But still there are 5 berths(at the time of writing this) available in 1AC tfor NDLS-GHY.Since ur child age is 9 years (child age) so even if you book the ticket till GHY,fare difference will be Rs 560 only.But you will get confirmed berth.Only thing i donot know is that whether you and your child will get berth in same cabin or not.may be you and your child get berth in different cabin(this may be possible in scenario of booking ur child ticket till GHY)