Westin is a good choice for a family stay. It is a solid hotel with larger-than-average rooms for Tokyo. My family stayed there last fall; they are very well-equipped to deal with children. They even supplied us with all the diapers we needed for free. And even the fancy restaurants in the hotel welcome children, which is far from universally the case in Tokyo.

The only downside to the Westin is that the concierge desk is not very useful. They will attempt to steer to you the least authentic, most westernized, lowest-common-denominator version of whatever you enquire about. I’ve had far better experiences with the concierges at other high(ish)-end proprieties in Tokyo. This could be important to you depending on your interests, because many reservations in Tokyo are logistically difficult to impossible for non-Japanese speakers.

That said, the only other hotels I could recommend in Tokyo for your situation would be outside of the Starwood universe.