Try using the barbecue in the park for thirty minutes. It gives you one-hundred XP's per sim. (You can keep barbecue with a lot of sims because it only takes thirty seconds to cook it until they sit down to eat it) Plus, it's fast.
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If you have toddlers and you are going somewhere or going to sleep, just make them watch a marathon on a TV.
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It helps if you have a lot of sims, I have eighteen but I'm on level twenty-six.