Turns out JR did write about two different toys in each of his books.
From The Death of Innocence:
"Meanwhile, I went downstairs to try to get Burke to come up to bed, but he was deeply involved in assembling the miniature parking garage he had received that morning. I could tell he wasn't going to go to bed until the project was finished, so I settled down on the floor beside him. Helping him complete what his mind was focused on was the best way to get us both in bed quickly."
From The Other Side of Suffering:
"Burke plays downstairs by the Christmas tree. He's trying to assemble a mechanical robot made of the Legos he got for Christmas so I sit down on the floor to help him put it together, but it's way too complicated for tonight."
From JR's BPD Interview (April 30, 1997):
TOM TRUJILLO: Okay. (inaudible) Lets go back to the 25th, sorry about that. Get home about nine, nine-fifteenish, Burkes downstairs playing; do you remember what kind of toy that was?
JOHN RAMSEY: Oh, it was a little thing that kind of unfolded, and it was like car ramp or something and then it folded all back together and it made something else.
TOM TRUJILLO: Was it like (inaudible) . . .Was it like putting stickers on it?
JOHN RAMSEY: Well, it was a plastic thing he had to assemble and he had some stickers too, and uh, he was intent on getting it done before he went to bed, so...
TOM TRUJILLO: Did you help Burke get into his pajamas that night?
JOHN RAMSEY: Yeah, like I do every night.
(If I'm correct, it seems as though he's speaking about the miniature parking garage toy in this interview).
To answer your question, I don't think that this was the most important inconsistency that the Ramseys have conjured up, but I think it's interesting because I would think that someone would remember every single little detail about the night one of their family members was murdered. I would understand completely if it was just a minor error that isn't that important, such as this one, but when almost all of the Ramseys' interviews are filled with a bunch of "I don't know"s and "I don't remember"s, every inconsistency of theirs, big or small, makes me wonder what the truth of the matter really is.