We've learned the children have lawyered up over John's estate, which is reportedly worth around $35 million. John's mom, Shelia Ward, filed his will in probate court last Friday, leaving all of his property to Justice, his firstborn.

Here are the major problems. The will was drafted in 1993 when Justice was John's only child. John left everything in his will to Justice.

Singleton had a total of 7 kids at the time of his death. The will never accounted for the additional 6 children. Under California law, unless the unborn children were specifically disinherited in the will when John signed it, they may have a legal claim to a portion of his estate. And, no such clause exists in the will.

Shelia is the executor of John's will, and when she filed her legal docs she listed his assets at around $3.8 mil. That means more than $31 million is unaccounted for. Most likely, John created a trust with assets that don't have to go through probate court. In other words, it's all taken care of outside the will.

We don't know who gets what in the trust ... because trust documents don't have to be filed in probate court. But, that is clearly the bulk of John's estate.

We know at least one of John's kids is furious at Shelia because while he was in a coma, 21-year-old Cleopatra accused Shelia of trying to cut all of John's kids out of his estate.

In addition to challenging the will, the kids could file a separate lawsuit if they have beef over the trust or whatever John created to dispose of the $31 mil. A legal fight may not just pit grandma against grandkids ... it could also pit some of the kids against the others.