Is it permissible for a Muslim mother to seek the help of a non-Muslim lawyer to regain custody of her child, and is it permissible for her to take Zakat to cover the legal fees if she and her husband are unemployed?

It is permissible for the parents to resort to secular courts and hire a non-Muslim lawyer to reclaim their right to the custody of their child. It is also permissible for them to receive zakat (definition) if they do not have enough for their sustenance or to rescue their child, as they fall under the category of the poor. Furthermore, rescuing a child from disbelievers falls under the categories of zakat expenditure, similar to freeing captives.