子供: kodomo. It makes great sense to include visions of children and childhood experience in a renku; the state of youth and innocence is a crucial and necessary phase of human existence. If possible, you should visit it at some point in your chain of verses. If you want to end with a note of optimism, save this theme for one of the last two verses.
And while you're brainstorming the topic of children, you might also devote a verse to that other extreme of life: old age.