Maxis and EA have confirmed already that they are ripping out some features that have been a part of The Sims for quite some time from The Sims 4. These features include the "Toddler" life stage and swimming pools. No joke, these have been a part of the series since the first game.
"It's not possible for us to include every single feature and piece of content we added to The Sims 3 over the last five years," said Ryan Vaughan, a Maxis Producer.

Also of note is that teenagers will be the same height as adults in The Sims 4. They are also removing the Create-a-Style feature that was quite popular from The Sims 3.

Even more interesting is this additional quote from Vaughan on the possibility of adding those features back into The Sims 4.
"While we recognize that some of you will be disappointed that pools and toddlers won't be available when The Sims 4 Base Game launches in September, you should know that we're building an incredibly strong foundation that is capable of fulfilling every one of your desires in the years to come."

Expect to see the "Terrible Twos" DLC to follow the release of The Sims 4 that will bring back toddlers. That will shortly be followed up with the "Summer Fun Pack" which will bring back pools. They will both retail for $19.99 (USD) each.