Plot hole: The timeline is off. Mummy started in 1923, yes, but it wasn't until three years later in 1926 that Evie and Rick actually met. Mummy Returns takes place in 1933 - only 7 years later, but they've got an 8 year old son. At that, Rick and Evie's son was born the year before they met...
Plot hole: The mummies that attack during the scene on the doubledecker bus are supposedly pretty tough and can smash through brick and masonry walls. However, during the fight just before the bus hits the bridge, the mummy fighting Fraser acts like a normal person. The two grapple together, and the mummy has his hands around Fraser's throat and tries to strangle him. Not only does Fraser fend him off, he even breaks his grip and dives to the floor before the bridge hits. Pretty wimpy for a mummy that just tore through a steel bus roof.