I've never come across this policy before but it makes sense. They just need to communicate it, which they should have been able to from your booking because you have to specify the ages of your kids.
Sofitels & Pullmans in Australia let kids in, I had my 2 (age 5 & 8) in many times, so it's strange to me that they would yet the Novotels which promote many family benefits, doesn't.