It is commendable that you are the sort of person who will respect his right to freedom of religion and not hold him back from attending and worshipping however be aware that the same respect will not be given to you or your child by him or anyone else in this cult.
Their collective mind set is "if you are not with us, you are against us and worthy of an imminent death at the hands of our loving creator at the great day of God the almighty.,"
He will be pressured to get you to convert and it will cause tension in your relationship.