The Netherlands, seems to have come up with a fair system for all the children of "blended" families:
"All non-resident parents in the Netherlands must support their children. Where possible, parents are encouraged to arrive at voluntary arrangements for child support. If an agreement cannot be arranged, a child support liability can be decided upon by the District Court, using the TREMA tables. These tables contain complex formulae for the assessment of maintenance, and take into account the following factors:
1.assessable income, which is calculated by deducting amounts for living expenses (based on social assistance rates) from gross income;
2.allowance is made for the non-resident parent's costs of setting up a new home and the costs of contact with the children;
3.where the non-resident parent has a second family, assessable income is reduced by around 50 per cent, in recognition of the belief that people should be free to form new relationships;
4.whether the resident parent has entered into a new relationship, the decision about liability for maintenance between a step-parent and a non-resident parent is based on an assessment of the relationship between the child and the non-resident parent. Deliberations canvass issues such as whose surname the child bears and how frequently contact occurs. "
Hopefully Canada will follow suit and make an allowance for "second family" situations.
Canadian Child Support Guidelines are Unfair to "Second" Families Petition