This is a very difficult issue. The Church has not yet pronounced anything on this issue. In some sense, we are free to propose our own solutions depending on how we see this question.
I agree with some people who have the opinion that, since aborted babies innocently died a violent death, they are, in a way, baptized by blood, and their death can be considered a baptism of blood. God took their souls into His eternal Kingdom and in His presence. In my opinion, this is possible.
For those children who simply died before they were born or those who died before baptism, in this case, the baptism of desire can be applied, especially when their Catholic parents genuinely desired baptism for their deceased child. This is similar to when a child is baptized, where parents substitute the infant's wish to be baptized, and the Church accepts the infant's baptism.
Analogous way, I think we can also apply this to the deceased children of those believing parents who desired baptism for them, especially those who died before baptism or those who died in the womb of their mother.
Analogously, I think we can also apply this to the [deceased] children of those believing parents who desire baptism for them, those who died before baptism, or those who died in the womb of their mother.