Police have raided properties and arrested four people over a children's birthday party brawl at a western Sydney play centre last month.

Officers are still hunting for another three people involved in the brawl.

Three fathers had to be taken to hospital with injuries when a fight broke out between adults attending the two separate birthday parties that were being held at Lollipop's Playland & Cafe in Wetherill Park on June 20.

The brawl, which was filmed on a mobile phone, was said to have started when children from each birthday party were using the equipment at the indoor playground for children, aged two to 11.