Fox's family sequel based on the Wimpy Kids books debuted at number one on an estimated $24.4m (£15m), the studio said on Sunday night. Meanwhile, Warner Bros' adventure fantasy Sucker Punch from Zack Snyder claimed the silver medal on $19m. That figure is going to have to climb considerably otherwise Warner Bros has a costly folly on its hands. That may not be so easy as spring brings a crowded lineup next weekend with the arrival of Summit's Jake Gyllenhaal thriller Source Code and Universal's family extravaganza Hop.

Speaking of next weekend, Harvey Weinstein and his cohorts are re-releasing The King's Speech in its new PG-13 version. The best picture Oscar-winner has been a sensation around the world and serves as a ringing endorsement of a vibrant independent sector that continues to consolidate after the financial crisis. It managed to gross $135m through the Weinsteins in its R-rated form in the US and has amassed a further $240m or so overseas, mostly through FilmNation licensees.

That said, this whole certification process has been nothing more than posturing. When the Weinsteins petitioned the MPAA ratings authority to lower the rating from R to PG-13, they argued that children needed to see the movie's message about overcoming adversity. The MPAA initially awarded the R rating in response to a sequence of expletives uttered by Colin Firth's character during speech therapy.

The Weinsteins can shout all they like about the story's relevance to the next generation, but really all they want is to squeeze as much money as they can from audiences. And hasn't every child who can be bothered to see a period drama already watched The King's Speech? I know plenty of friends' kids who have. On the other side, the MPAA's concerns illustrate an inconsistent philosophy. This is an institution happy to allow children aged 13 accompanied by an adult to witness weekly doses of blood and guts. That's because a lenient certification means more theatres will carry a movie and that's how the studios, whom the MPAA represents on Capitol Hill, make their money. Throw a few expletives into an otherwise well-mannered drama and the MPAA's puritanical, fuzzy thinking is exposed.

So the PG-13 version presumably contains fewer F-bombs and justice is served. Still, it's good to see the movie prosper because (a) it's very well executed, even if it isn't everybody's cup of tea and (b) it was backed in part by the moribund UK Film Council. We'll see a few more movies open with the council's support, including the Tilda Swinton drama We Need to Talk About Kevin, which may premiere at Cannes this summer.

North American top 10, 25-27 March 2011

1. Diary of a Wimpy Kid: Rodrick Rules, $24.4m

2. Sucker Punch, $19m

3. Limitless, $15.2m. Total: $41.3m

4. The Lincoln Lawyer, $11m. Total: $28.9m

5. Rango, $9.8m. Total: $106.4m

6. Battle: Los Angeles, $7.6m. Total: $72.6m

7. Paul, $7.5m. Total: $24.6m

8. Red Riding Hood, $4.3m. Total: $32.5m

9. The Adjustment Bureau, $4.2m. Total: $54.9m

10. Mars Needs Moms, $2.2m. Total: $19.2m