You and your spouse have both taken up qualifying jobs. You have two qualifying children and are allowed to claim the additional Child Tax Allowance. You pay €3,000 towards the children's upkeep and your spouse pays €1,000.
The allowance for your two children in Year 1 is €2,540 (€1,270 x 2).
Self €2,540 @ 75% = €1,905 x (€3,000 / €4,000)
Spouse or civil partner €2,540 @ 25% = €635 x (€1,000 / €4,000)
You can jointly decide to let one of you claim the full child allowance or have the allowance split between you in another way.