Finally, I booked separate ticket for them which was in WL and got confirmed on day of journey in same coach.
Even though, I had booked half ticket for 5 year child , it was refused to serve by catering staff but then I showed name in chart with Non-veg as food option. The argument was as no seat present so no food then I asked to call catering manager. No one turn up but after 15 min, he served food for child.