The most common cause of leakage is fitting your baby with the wrong diaper size. So start by checking if the diaper size is right for your baby. Note also that the amount of pee increases as your baby grows. By the time your baby is 12 months old, the amount of pee discharged in a day will be twice that of a newborn. While the diaper size may appear to fit your baby, the amount of pee may have increased with his growth, so the diaper may not be able to absorb the larger amount of urine. For disposable diapers, the bigger the size, the better the absorbency. If you notice frequent leakages, it may be time to change the diaper to a larger size.
If there is leakage even though you have fitted the diaper properly on your baby, do a check for the following:
Why is baby's diaper leaking?
Advice for leakages from different parts of the diaper
When placing the diaper under baby's bottom, make sure you pull the diaper high enough to prevent leakage. Raise the back portion slightly higher than the front portion and then fasten the tape diagonally downwards.
Make sure that the diaper edges are not folded and that the tape is fastened evenly. If you notice that the position where you fasten the tape is out of the marked area, it's time to change the size of the diaper. Try using one size bigger.
Pull the diaper straight and high enough to reach the belly button area. Adjust the gathers around the leg area so that they fit properly around the crotch area. Make sure the gathers are pulled outwards. If the leakage continues even after your child has been strapped on with a seat belt, try to fasten the diaper tape at a lower level, slightly slanted at an angle.
Raise the front portion of the diaper slightly higher than the back portion and fasten the tape slanting upwards so that the belly button is hidden. For boys, make sure the penis is pointing downwards.