According to tokyo hyatts thread wiki - not sure if still current...:
All allow 2 adult with 2 kids <12 yoa in base room. They clear state "Guests at this location are considered children between the ages of 0 and 12. Any guest 13 years of age or older will be considered an adult and will be subject to adult pricing."
i stayed there with two kids in a suite but kids were 2 yo back then..
i have atrium suite booked this time and plan to either email them or just show up...