here we have a 'sleeping child' by the Italian baroque painter Bernardo Strozzi. the painting can be found at the Residenzgalerie in Salzburg which perhaps explains why it is on an Austrian stamp for the theme 'old masters' (2012)
and the wide awake faces of the three daughters of King Willem-Alexander: Catharina-Amalia of Orange (right) and her sisters Princess Alexia (left) and Princess Ariane (middle)
and from Finland, this stamp for the theme of agriculture & food and games & toys was issued in 2010
see more children themed stamps here