@Morgann1104 While many families share one Origin account, especially among children, it's technically against EA's terms of service. So yes, it would be best if you created a new Origin account for your younger daughter. That will also allow the kids to play at the same time if they want—Origin doesn't allow one account to be logged in and online on two different computers at the same time.
Since the Sims 4 base game is on sale for $5 U.S. for a couple more days (or $6 for the Digital Deluxe), it's a good time to buy a second copy.
By the way, there are restrictions on buying content for child accounts, which you may want to look into before choosing the birthday on your daughter's account. For example, the way it works now, you wouldn't be able to gift her a Sims 4 pack; you'd need to buy it in a store, for full price, and register the code on her account. Hopefully that will change soon, but in the interim, it's a huge headache to try to add content to a child account.
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I don't work for EA. I'm just trying to help fellow players with their games.
