After you purchase and download the GP, there should be the maxis pre-made restaurants in your library. You can also build your own or find more on the gallery (you can choose restaurant under the venue options like you would for a bar, gym, park, etc. If none of these things are showing up, make sure that the pack has downloaded/installed and is listed with your other packs.
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Also are you using mods or cc in your game ?
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Ideas on how to improve babies.