I read the other 3 reviews - yes the acting is bad, but that is only if you are holding it up to much better work. The main character (who seems to have 10th billing) is Abe, a supposedly OLD GRUMPY Guy who neither looks "old" nor realistically pulls off "grumpy", but remember that I am an adult seeing this through the adult eyes a an avid movie buff.
The film has its moments - though admittedly they are few. If I was a young child this film would probably be quite good. In fact my expectation is to watch this with my 3 year old grandson who I think will find it quite enjoyable once someone watches it with him and explains things as the film progresses. I have the feeling it will be a movie he will want to watch often.
Unfortunately, from the adult viewpoint the acting is restrained like in the opening scenes where Abe is running away from what we quickly find to be Bruno the ape but he isn't really running - he is just sort of giving the impression that he could be running. Again, an adult look vs. a child's eye view probably makes the world of difference.
There is also a lot of what seems like attempts at comedy for the sake of making the film palatable for any adult who might have to supervise the youngster watching the film, like when Abe corrects his leaving the toilet seat up to appease Bruno's sensibilities on this subject.
This is basically examples of what to expect from "all" of the acting in this film, not just the actor portraying Abe. As an adult you'll find that the actors are acting, waiting for each other's lines and the occasional opportunity to step on someone else's line.
I was actually a little amazed that the three kids in the film got top billing as the Abe character and a few of the other adult actors seem to be the main characters, but that is just another example of who this film is geared towards.
As a film that I would categorize as an "After School Special" candidate for mid-western (I would have to drop it a few points for either coast) pre-teen family viewing I rate this at the higher end of the spectrum. If I was rating it for my own viewing pleasure I would unfortunately have to give it a flat out zero.