The prequels were going to be dark. Assuming that all 3 had been written, or that the core audience (including kids) knows what happens to this kid, a "lovable" marketable "friend" for Anakin probably seemed like a good investment for toy sales alone. If you haven't already, watch The Phantom Edit, which cuts out Jar Jar (almost) completely and makes other changes. Episode 1 is probably the darkest of all 6 because it's just happening to an innocent kid. Plus nobody wants to buy Liam Neeson toys.

The only thing in the whole prequel trilogy I liked was the scene where Jar-Jar is using his tongue lizard-style to snatch food off the table and Qui Gon Jinn (Liam Neeson) grabs the tongue in midair and in his best menacing growly voice says, "Don't do that again."

That should have happened more often.