Smothens the infant care interactions.
lesscheckoninfants - Sims will react better to their baby and will not check on them quite as often (they will still do so, though). The same also applies to newborns.
needs - less diaper blows, high chair foods will raise hunger more, infants will need less sleep once they have certain milestones
milestones - accelarates especially the crawl and pull up to stand milestone.
socials - fixes some oversights with some infant-related social interactions beetween older Sims and also adds speech bubbles for those.

Makes burnouts less of a nuisance.