I have noticed two slip-ups in the Rugrats. Here's the 1st:

After being separated from the rest of the babies in the forest, tommy and dil are snuggling up to sleep (just after they fought off some monkeys), and dil is covered up with half of the torn blanket. on this half, you can clearly see the picture of the top half of the bear (the other half of the bear is on the other half of the blanket), which has its head pointing upwards, towards dils head. Then, a few seconds later, tommy lies down next to dil, and dil covers tommy with the lower half of the blanket (this is the half with the bears legs). then you'll see the that the half of the blanket on dil has somehow magically turned 90 degrees, so that both halves of the bear picture match up. Kinda strange that dils half of the blanket could turn itself 90 degrees, huh?

Slip up No 2

A bit later on in the movie, just after Stu crashed into a helicopter in his flying machine and they kicked him out of the helicopter, you'll see Stu flying again, but his propellers fall of. then a couple of minutes later, just before Stu crashes, you can see that the 2 propellers are back were they where before they fell off1 pretty strange huh?