Here is my best attempt at compiling all these in one place. Take a look for yourself and you be the judge. Is she a bad parent?

1. April 2006, Sean Preston falls out of high chair and hits his head. The babysitter is blamed.
2. April 2006, Britney drives with 8 month old Sean Preston on her lap.
3. April 2006, Britney is alleged to worry that Sean Preston has suffered brain damage from the 2 or 3 times he fell out of her bed while he was sleeping with her.
4. May 2006, Britney is spotted driving with Sean Preston in a forward-facing carseat. Not illegal under CA law, but ill-advised.
5. May 2006, Britney stumbles outside a NY hotel while carrying SeanPreston, nearly dropping him.
6. December 2006, Britney begins spending alot of time with Paris Hilton, partying. Paris defends her saying “partying has not come in the way of her parenting.”
7. July 2007, Britney and her kids squat at a Pacific Palisades CA home they toured as part of a real estate deal; a home on the market for $6.5 million. They eat tacos and mess up the furnishings, Britney’s bodyguards even going to her home to retrieve some of her belongings and bringing them back to the home.
8. July2007, Britney takes her kids for a boat ride in Marina del Rey; the children do not wear life jackets.
9. July 2007, it is reported that Britney has her sons fetch her cigarettes from around the house, calling them “Mama’s lollipops.”
10. August 2007, DCFS investigates allegations of poor dental hygiene, eating and sleeping habits of Britney’s children. It is alleged that Britney tried to get a LA dentist to whiten Sean Preston’s teeth, rotting from Baby Bottle Syndrome.

Throughout this time period it is alleged that Britney passes her children to body guards and nannies, rarely spending quality time with them, drinks, uses drugs, swears, feeds her children junk food, does not keep them on a schedule of naps/bedtimes and isolates them from their extended family due to her conflicts with these people.
In the category of odd, but not directly affecting her children:

1. June 2006, Britney does an interview with Matt Lauer of “Dateline.” She acts erratically, chews gum, looks disheveled and sobs.
2. November 2006, Britney is seen dancing at a Las Vegas club, without pants. She was hot, reportedly, and took her pants off to cool down.
3. December 2006, over the course of a few weeks Britney is escorted out of a LA club for erratic behavior and is photographed several times wearing short dresses and no underwear.
4. February 2007, Britney shaves her head in a Tarzana CA salon.
5. February 2007, Britney enters rehab. twice.
6. March 2007, Britney enters rehab. Again.
7. July 2007, Britney strips to her underwear and splashes in the ocean near Malibu.
8. July 2007, Britney storms out of an OK! Magazine photo shoot after letting her dog poop on a $6k dress, peeing with the bathroom door open, shrieking at the staff and walking away with clothing and accessories that were not comps.
9. August 2007, Britney hits another car in a parking lot and leaves the scene.
10. August 2007, Britney is seen in Beverly Hills wearing a shirt as a dress…no pants, questionable on the underwear.
11. Sept 2007, a dazed-looking Britney dances and lip synches her way through her “comeback” performance at the VMAs.
12. September 2007, Britney’s former body guard claims to have witnessed her using cocaine at least twice.

I think the evidence points to the fact that she lacks common sense and does not put her children’s needs ahead of her own desires. Is she the worst parent ever? No. Those parents are listed here. But she does seem ill-prepared to take care of her children and does need help.