There is a mighty supposition at work here, the idea that "we are guaranteed heaven before birth". "If" that is the case, then the rest of the question logically follows. But if the supposition itself is unfounded, then the rest of the question evaporates. So, the only sensible way to tackle this question is to check out the first part first.
Yes, "Some Christian traditions believe that all infants go to heaven." Though it needs to be pointed out that the Presbyterian Westminster Confession of Faith qualifies that with "elect infants", meaning that "non-elect infants" are not deemed to be 'regenerated' i.e. 'saved'. Therefore, those Presbyterians cannot be included amongst other denominations that believe in what can be termed "Universal Charity". This holds that God's love is not discriminatory, but extends to everyone, who will eventually be saved. Logically, that would include infants, and even those in the womb.
Those who believe this might say that dying at a very young age will not (in a sense) matter, as eternal salvation is sure to them. But I have yet to hear any from that school of thought claim that "it would be better to die early rather than risk damnation". It only takes a second's though to realise that that is a contradiction in terms. If all will eventually be saved, there can be no such thing as "risking damnation".
Obviously, all who believe God does discriminate between repentant sinners and non-repentant sinners, so that he judges the latter, who will be kept out of heaven and so suffer eternally outside of his love, cannot subscribe to Universal Charity. They must be viewed as distinct from those who do; those who seem inclined to suppose that all babies and toddlers automatically get into heaven. It may also turn out to be the case that William Lane Craig would never subscribe to the "better to die in infancy than risk eternal damnation" school of thought. I don't know anything about him, however.
The two quotations offered do not actually prove that either example fits the bill here. The view seems to be that of the OP who says, "In this view, wouldn't it be better if everyone died before they are born, so they avoid becoming sinful, and thus guaranteed to go to heaven?" Now, if quotations could be given from groups in Christianity where that is their view, the question could be fully answered. As it stands, the answer I offer is, There is no "guarantee of heaven before birth" in the Bible, but even those who think there is may see a disjunction between that and thinking that living longer could risk damnation.
Many Christians who do not subscribe to Universal Charity would say that damnation is not a risk - it's guaranteed, unless repentant faith is placed in what God alone, in Christ, did to save us from damnation. As the God of all the Earth is deemed to always judge righteously (Genesis 18:25 & Revelation 19:2), what happens to babies and toddlers will be under his sovereign outworking when it comes to matters of eternity. The only response I can make to the latter part of the question is 'No', for it does not logically follow that dying early avoids the 'risk' of damnation.