I reported this on the official bug forums on May 23rd:
http://answers.ea.com/t5/The-Sims-4-Bug-Reports/Children-can-no-longer-chat-on-the-jungle-Gym/m-p/4558272#U4558272In my game, children on the jungle gym (pirate ship) at the same time are unable to perform directed chat interactions.
If they start the conversation while one of the children is still on the ground, the conversation will continue, autonomously, once both children are on the pirate ship but I then can't choose any specific chat interactions.
Anyone else experiencing this? If so, please use the Me Too button in the top post on the official bug post I linked above. I noticed this after the May patch.