Street Fighter III series
A three years old Mel appears in Ken's ending, where he wishes to follow in his father's footsteps and trains with him.
Street Fighter IV series
In the Street Fighter IV games, Eliza is pregnant with Mel. He is born in Ken's Super Street Fighter IV ending.
Street Fighter V
Mel appears with his parents in the prologue, the Masters family being invited to a party hosted by Karin. He pass most of the time sleeping, but awakens during Ken's fight with Karin.
Although Mel doesn't appear, Eliza gets pregnant before the second Street Fighter tournament is announced (thus, earlier than in the games' timeline), and she and Ken soon get married.
Street Fighter IV: The Ties That Bind
In the OVA, Eliza has just found out that she was pregnant but hasn't told Ken yet. As she's getting ready to give him such good news, that she is also captured by Crimson Viper in order to lure Ryu in for Seth. In the end Ken manages to rescue her in one piece, and she tells him that he's going to be a father.