Munchkin Inc., a North Hills manufacturer of baby and toddler products that got its start making novelty baby bottles, says it makes the best diaper pail on the market.

But Playtex Products LLC in Westport, Conn., a major competitor in the baby products business, won’t hear it. It said Munchkin’s testing methods stink.

So began what’s turning into a pitched battle between the two companies. In January, Munchkin sued Playtex in federal court in a preemptive strike to retain its diaper disposal product’s advertising. The case was expanded to include a Munchkin countersuit over Playtex’s sippy cup product in May. The whole matter is scheduled to go before a jury trial in April.

It all started in November of last year when Munchkin performed a laboratory test to prove that its diaper disposal product, the Arm & Hammer Diaper Pail, better contains odors than its competitors’ products. The company began putting stickers on the diaper pail’s packaging that labeled the product “The New No. 1 in Odor Control,” claiming it was “Proven Better at Odor Control than Diaper Genie II & Diaper Genie II Elite.”

Those are references to products by Playtex that often sit next to Munchkin diaper pails on store shelves.

Munchkin in January heard from an attorney for Playtex, who demanded Munchkin remove the stickers or face legal action, according to Munchkin’s lawsuit. Playtex claimed the laboratory tests were flawed because they didn’t use real soiled diapers.

But Munchkin didn’t wait and filed suit against Playtex just days later demanding that Playtex stop its “threats.”

Then in May, Munchkin took issue with advertising Playtex was using to market its spill-proof toddler cups. Playtex claimed it had the “No. 1 Spill-Proof Cup.”

“Playtex makes this bold assertion on its cups without evidence or data to support the claim that Playtex has the ‘No. 1’ cup in controlling and containing spills,” the lawsuit states.

Munchkin makes a competing product that it believes is just as spill proof.

Competition between Munchkin and Playtex began 20 years ago when Steve Dunn founded Munchkin to manufacture novelty baby bottles.

“There was only one company making decorated baby bottles at the time, a company called Cherubs,” Dunn told the Los Angeles Business Journal in 2001. “I contacted Cherubs with the thought of trying to acquire them and then using my concept.”

But before Dunn got anywhere with Cherubs, he got news that Playtex had acquired the baby bottle company first.

“I took that as a sign that I was on the right track,” Dunn said.

In 2006, the Business Journal reported that the then-15-year-old Munchkin had 73 percent revenue growth over a two-year period. And this October, Dunn said in a press release that Munchkin had “intense growth.”

A spokeswoman at Munchkin said executives were not available to comment for this article. Playtex did not return phone calls. Attorneys declined to comment.