Should the money found in the box in the deceased's home garden be distributed as inheritance or equally among his children?

If the money has no known owner, it is either a rikaz (treasure) from pre-Islamic times, in which case it belongs to the owner of the land (the heirs, in this case), according to the majority of scholars. Or, it is from the Islamic era, in which case it takes the ruling of luqatah (found property), and must be publicly announced for a year.