Under certain circumstances the decline in fertility might not matter. A falling population would mean falling home prices, labor shortages and hence increased wages. Such effects, by easing the struggle for existence, would tend, in time, to restore the birth rate to or beyond the replacement rate.
However, the Western governments have adopted a program to destroy their own people. They have repressed the fertility of their own people while inviting masses of people of alien races, religions and cultures into the already densely populated European lands. The Western nations under the leadership of fools and traitors, are committing suicide.
In addition, the Western nations have policies of education, taxation and welfare that promote reproduction of the least productive members of society, while inhibiting reproduction by the most capable members of the community.
So for the European nations to restore their populations while favoring the reproduction of the most able members of society, they must begin by eliminating their existing dysgenic programs. That means slashing welfare, particularly in support of unwed mothers and the often unemployed males that impregnate them.
Having cut welfare spending, governments can then cut the huge burden of taxation on the most productive members of the community. As a start, there should be something like a $50,000 tax break for every child. That would not affect the poor and the unemployed who pay no income tax, but it would be a big deal for those in the higher income brackets, who, for the most part, represent the more able members of society.
With such a tax benefit, a married woman, by having babies, might save a high-income husband much of what she could earn on her own. In any case, the saving would amply cover the cost of good quality daycare, if she wished to go out to work while raising a family.
To make the incentive even more effective, the tax break should be delivered in the form of a cash payment to the wife.
In addition, there should be an end to anti-reproductive propaganda in schools, e.g., the pro-queer/trans agenda, and the instruction in sexual perversion from kindergarten on up. At the same time the stigma attached to illegitimacy should be restored. That won't prevent young unmarried girls getting pregnant, but it will make them more careful, with the result that they are more likely to be impregnated by the better class of male (i.e., the one they really can't resist because he is truly a very attractive fella*). Moreover, the father of every illegitimate child should be identified by DNA profiling and compelled to make child support payments.
In addition, and of vital importance, immigration to the European nations should be cut to zero. That way resources, particularly housing, schools and hospitals, would be freed up for the native population, thus lowering the cost of living, the rate of taxation and the stress of life, while driving up wages. The result would be a hugely more family-friendly economic environment.
* For the British, and probably the rest of Europe, this would be a return to the traditional mode of working class reproduction, as in the 1950's for example, when one third of all conceptions in Britain were out of wedlock. And as Shakespeare put it, this must have been more or less the situation back in the 16 Century:
It was a lover and his lass,
With a hey, and a ho, and a hey nonino,
That o’er the green cornfield did pass,
In springtime, the only pretty ring time,
When birds do sing, hey ding a ding, ding;
Sweet lovers love the spring.