I haven't heard anything about another Chrono sequel...
(SPOILER)As for Chrono Cross, Kid was the clone of Schala from Chrono Trigger. Lucca (whom Kid calls "sis") found her in the forest with Schala's pendant and took her in as well as other orphans. Lynx burned the place down and Lucca was killed (you see Crono, Lucca, and Marle's spirits as the children in the Dead Sea). Also, you get to see childrens' drawings of all of the playable characters in Chrono Trigger except for Magus inside of Lucca's house (which is almost the same in Chrono Trigger as it is in Chrono Cross except with a few new rooms) when it's burning and you have to save young Kid from it. Lucca also sends Kid a letter that Luccia gives to Kid which mentions Janus (Magus). One thing that always puzzled me though, was how could Glenn (Frog) be 24 in Chrono Cross when he was probably already that old in Chrono Trigger and Chrono Cross takes place 20 years after the events in Chrono Trigger? Besides the fact that they messed up Glenn's past in Chrono Cross. Oh well, I guess I'll never know.