Like the first sonnet, this one also urges haste in procreation. This makes me think of all of those commercials for contraceptives that show all of the pleasures you can enjoy by not having kids. It is amazing when speaking to teenagers about how one day most of them will be parents I receive blank stares of incomprehension back. The idea of being a parent is so alien to them, even as they imagine themselves as adults (for children tend to imagine adulthood as childhood, but with more freedom).
But the poet, speaking from experience I think, explains that there are deeper and higher beauties that having children brings.
When forty winters shall besiege thy brow,
And dig deep trenches in thy beauty's field,
Thy youth's proud livery so gazed on now,
Will be a totter'd weed of small worth held:
Then being asked, where all thy beauty lies,
Where all the treasure of thy lusty days;
To say, within thine own deep sunken eyes,
Were an all-eating shame, and thriftless praise.
How much more praise deserv'd thy beauty's use,
If thou couldst answer 'This fair child of mine
Shall sum my count, and make my old excuse,'
Proving his beauty by succession thine!
This were to be new made when thou art old,
And see thy blood warm when thou feel'st it cold.