Hi,

Please refer to the code below:

from odoo import fields, models

class MrpProduction(models.Model):
    _inherit = 'mrp.production'

    new_field = fields.Char(string="New Field")

    @api.constrains("new_field")
    def _constraint_new_field(self):
        child_mo = self.self._get_children()
        for child in child_mo:
            child.new_field = self.new_field

Hope it helps.