From jwfacts:-
Children
Child dying at Armageddon - Enjoy Life Brochure
Children are considered to share in the sins of their parents, so babies will die at Armageddon if their parents are considered unworthy of salvation.
"What will happen to young children at Armageddon? The Bible does not directly answer that question, and we are not the judges. However, the Bible does show that God views the young children of true Christians as "holy." (1 Cor. 7:14) It also reveals that in times past when God destroyed the wicked he likewise destroyed their little ones." Reasoning from the Scriptures pp.47-48
"Children are affected by the course of their parents, and parents are warned that their iniquity is visited on their offspring unto the third and fourth generation. (Ex. 20:5, 6) Parents are commanded to instruct their children in God's way, and if in these last days parents refuse to heed the divine instruction and warning they bring destruction upon themselves and their small children at Armageddon. (Deut. 6:6, 7; Eph. 6:4) According to justice God can leave such children dead, for, as Ezekiel showed, all die in their iniquity." Watchtower 1950 Nov 15 p.463 Questions From Readers
"By all the evidences this system of things is hastening to its final confrontation with the God of justice at Armageddon. Parents and children who fail to gain the "mark on their foreheads," that is, an adequate appreciation of God's moral standard, are sure to suffer. Parents will be held accountable for their children, and children will suffer for the failure of their parents." Watchtower 1968 Feb 1 pp.83-84
George