Living or Guest

Classified by who? The state, their school, the landlord? Might need to clarify your reasons in order to get a useful answer

Children can't be party to a tenancy agreement and so can't request to be added to a tenancy even if they are licensees, so from the landlord's perspective it is immaterial. Really the only concern for the landlord would be whether their occupation of the property would make the property overcrowded under the definition in the Housing Act 1966.

Edit: If the landlord's notion is that the children's part-time residence there would violate some clause in the tenancy agreement prohibiting taking in licensees and allow them to terminate the tenancy on that basis, they'd do well to read up on the Equal Status Acts, particularly the bits about discrimination on the basis of family status, because that isn't going to fly with the RTB or the WRC.

Most people would probably describe them as living there part of the time. If the kids were at boarding school during the week and back at weekends. There is no question that they live there, right.

But "classify" is a strange way to describe it. I don't think landlords should be concerned with classifying the domestic arrangements of their tenants. They rent a two bed apartment, the whole apartment, it's theirs to use as they need.

It's unlikely any sort of occupancy clause from the landlord is enforceable. Unless the tenants specifically offered terms for reduced rent.

Yeah but, as already pointed out, a tenant's minor children are never named on the lease, but there is no practice of tenants seeking the landlord's permission to have their children live with them. Nor, if they are blessed with further offspring, do tenants contact the landlord to seek approval to bring in an additional resident.

In short: good luck trying to get any court or tribunal to accept that a term of this kind applies, or can be applied, to the tenant's minor children. The right to have your minor children live with you comes as standard.

The Equal Status Act has already been mentioned. In general, it forbids discrimination on the grounds of family status. A carve-out allows you to discriminate if you are providing accommodation in your own home, but if you are renting out a self-contained flat you can't do that on terms that disadvantage tenants with children.

As Dav10 point out, the problem here is not the children; it's the lack of adequate soundproofing. AllForIt is either unduly sensitive, or (more likely) is living in a substandard building. I get the impression that the same landlord is renting out both flats — one to AllForIt and the one above to the tenant whose children live there part-time. This is very much the landlord's problem, but it's not a problem he can solve by telling the upstairs tenant that they can't have their children living there, any more than he can solve it by evicting AllForIt and letting to a new tenant who is aware of the problem and takes it on. The proper solution is the provision of better soundproofing.