For parallel charging, if you are using a low charge rate (1C or 2C), then it should not be an issue. As an aside, I always charge at low rates, just for battery pack longevity.

If you the packs have a substantially different charge rate capability (say for example 2C and 5C), then the pack with the lowest charge rating will determine the maximum parallel charging current (2C)
Same holds true for serial charging (if you're using a Cellpro 10XP for example). The pack with the lowest charge rating will determine the maximum charging current.