Don't know about Sweden, but here in France you are taxed as a family.
There is no PAYE, you declare your income once a year, then receive a bill a few months later. After the first year, you can pay installments based on the previous year's amount, so it's not just one lump sum to fork out.
Basically, all the family's income is listed (both spouses/civil partners plus any income kids may have from part-time work, trust funds etc.) and then the total is divided by the number of points the family is entitled to. Each adult is 1 point, the first two kids each count for 0.5 and any further kids a whole 1 point. There are additional points for disabled children, or war-wounded adults.
The amount "per share" is then taxed, according to a sliding scale and then any tax deductions/refunds are added/subtracted on the amount payable.
So, a family, with one person earning 10K and the other 50K, with 2 kids, would have a total income of 60k and 3 points, so the net tax base would be 20K, which would probably be subject to around a 15% tax rate, so roughly ?3000. A tax refund for 50% of childcare costs and domestic employee salaries would then be deductable from this, along with other "tax-rebate" things such as installing ecologically friendly heating systems, loft insulation or double glazing...