Britney Spears' child-care techniques seem to be growing positively "Toxic" — she nearly dropped her 8-month-old son on his head yesterday as she tottered out of a posh Manhattan hotel with a glass in one hand and the tyke in another.

The baby-bobbling bungle began at about 6 p.m., as the "Not That Innocent" pop tart left the Ritz-Carlton Hotel on Central Park South, holding her kid, Sean Preston, and what witnesses said was a tumbler of water and ice.

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While heading to a car, her long pants appeared to get tangled in her open-toed shoes just as she stepped past a pothole, witnesses said.

Then — oops! — Britney started to tumble. Sean Preston's head whipped back in what a witness called a "violent manner," his chubby arm swung up and his little hat went flying off .

"Her bodyguard had some good reactions," an onlooker said of the quick catch . "[He] grabbed the baby before he hit the floor."

Despite the tumble, Britney managed not to spill a drop of her drink. Then she muttered to fotogs in her Louisiana accent, "This is why I need a gun."

The incident left her clearly shaken up — afterwards she was seen in tears at FAO Schwarz.

Britney's people said they were unable to comment last night.

The near-drop is the latest motherhood woe for Britney, who dangerously drove with Sean Preston in her lap and strapped him into his car seat facing the wrong way, as The Post reported . He also fell from a broken high chair.