The animal onesie event is coming to Sims Freeplay. To be able to do this event you need to have completed the puppy odyssey discovery quest.
If you haven’t already found out how to start it, you go to the park, find the puppy and click the icon above it. You need to have completed this quest, because it unlocks the puppy hobbie that you need for the quest. This event is also time limited.
You will win amazing animal onesies for your sims, if you finish this event.
A.M Plays Sims 