So, I have been trouble trying to make my Sims stay in their seat. All of a sudden, a bubble appears over them and get up and they have an interaction such as "Tell Funny Story" and "Check Out New Object". I can't make my Sims stay in their seats. In the Sims 2, they always stay in their seat. But now, in the Sims 3, they won't stay in their seat and just keep on getting up. What is going on? How can I make my Sims stay in their seat and not keep on getting up just like in The Sims 2?

When the free will is enabled, the simmies in Sims 3 don't tend to stay put for very long. It's quite normal. If you need your sim to stay put in their chair for a longer perios of time (for pics etc.), you have to turn the free will off from the game settings.

So, will it be just like the Sims 2? Without having thought bubbles appearing which makes them get up?

Well, I take a lot of pictures and even though I have the free will off while doing that, the simmies still get though bubbles every now and then. I just wait for them to vanish and then press pause + take the pic. Or I use a cheat code to keep them away as long as I need: http://sims.wikia.com/wiki/List_of_storytelling_cheats