What is the ERC (European Research Council)? Find more information here:

-ERC website
-Euresearch: the Swiss guide to European research & innovation

Eligible career break: Children, twins... - how does it affect the eligibility time window?

The rule is to be interpreted literally, i.e. as "18 months per child", not as "18 months per birth".  In case of twins, the eligibily time window can be extended by 2 x 18 = 36 months.