It seems like you're looking for edition here. The only way "addition" would be correct is if you were adding something to the stroller: a basket, a cover, a decoration, a baby.... One way to remember might be that you could buy the newest edition of a stroller for the newest addition to your family.
Also, remember that the prepositions following the words differ. You'd say "newest addition to" something, vs. "newest edition of" something.
Here are some sentences to illustrate:
- The newest edition of BabyCo's ProBuggy stroller can fit easily into the trunk of any car when folded up.
- The newest addition to baby Lily's stroller was a plush turtle on a keychain above her head.
- "We don't need the newest edition of some expensive luxury stroller," said the new mother. "A tried-and-true secondhand stroller is just fine."
Hope this helped!
Edit: oops, didn't notice the date up top... oh well, maybe this will still help someone. :)