Is it true that whoever dies before puberty enters Paradise, and does not enter it except with their parents, and is it permissible to supplicate for them to die before puberty for this reason, or is it better to supplicate for them with a long life and righteousness?

Whoever dies among the children of Muslims before puberty is in Paradise, and this is a matter of scholarly consensus. As for the children of polytheists, there are three opinions concerning them, the soundest of which is that they are in Paradise. Accordingly, any child who dies, generally, before puberty is in Paradise.

It is not permissible for parents to supplicate for the death of their child, whether before or after puberty, because the Prophet (peace be upon him) forbade it. Rather, they should supplicate for their child's guidance, righteousness, and a long life in obedience to Allah, and strive to raise them with a righteous upbringing.