I am not familiar with MO properties so I can't comment. However I have stayed at the Westin KL around five times in the last couple of years. The Westin KL have both the hotel tower and the residence tower, so if you need a room large enough for a family, then consider staying in the residence wing in a 1 bedroom apartment, maybe 2 if you want to.
I usually stay in the hotel tower, but my last visit I stayed in an apartment and it was around 65sqm in size. Apart from the bedroom with a small study area, it also had a separate living area, full kitchen, another study room, large enclosed balcony with dining table.
I don't have kids so can't comment on club lounge access.
However the lobby restaurant where the main breakfast is served is really impressive. The spread is so wide and of good quality.
The pool area is very reasonable for a city hotel.