Something else to consider here is who you are holding as the liable person, as that affects what reduction you are going to give.
If you consider the childrens home to be a care home under the Care Standards Act 2000 and are holding the owner liable by virtue of the Council Tax (Liability for Owners) Regulations (as amended) 1992 then class U exemption does not apply.
Class U only applies where the SMI person would themselves be liable.
[i:7f9399b42d](1) a dwelling occupied only-
(a) by one or more severely mentally impaired persons, where, but for this Order, either such a person, or a relevant person, [b:7f9399b42d]would be liable to pay the council tax[/b:7f9399b42d][/i:7f9399b42d]
If you are holding the owner liable then the best you could give would be 50% discount as the only resident would be disregarded.
If it doesn’t fall into the definition of a care home then you may have to consider if it is a dwelling in multiple occupation and therefore be holding the owner liable with the same end result of a 50% discount.