Charlie Sheen believes his young son was burned during a visit to his mother.

The actor's ex-wife Denise Richards has written to Los Angeles Department of Children and Family Services (DCFS) to inform them she can no longer care for four-year-old Bob and Max - the twin children of the 'Anger Management' star and his troubled former spouse Brooke Mueller - and along with the note she included photos taken before and after a visit to Brooke on July 26, with the later picture showing a large red mark on Bob's head.

According to TMZ, though Denise didn't state what the mark was, Charlie believes it was a burn sustained while in the care of Brooke or her mother Moira Fiore.

In Denise's letter to the department - which was obtained by - she described how the boys go into a ''zombie-like'' state and can become violent towards her daughters Sam, nine, Lola, eight, and Eloise, two, and also suffer from disturbing nightmares.

She also describes how, after seeking medical advice, she was planning to have the twins' behaviour assessed by a specialist - something which Charlie agreed to - but Brooke blocked the move, allegedly believing Denise wanted to make out she is a bad parent.

Denise wrote: ''After speaking with the boys' attorney it was explained that their mother would consider moving forward with an assessment, but wanted a doctor that I did not suggest. I reminded him the recommendation came from their pediatrician not myself. [name retracted] said someone else mentioned to him that I possibly wanted to take them to a doctor to get them medicated. Medication was never mentioned in any conversation that I had in discussing an assessment or anything else.

''It was also conveyed to me that their mother and her attorney felt that I was trying to find something wrong with the boys so that she can't get them back.''

In her letter, the 'World is Not Enough' star criticised the fact that Charlie is unable to take the boys to school or spend time in her home with them.

She wrote: ''Charlie has been off work the last few weeks. During that time he's taken our daughters to school most days and picked them up. Because I have to be his monitor he's not allowed to take his sons to school...

''I'm now not permitted to have their father in my home while the boys are present, which at this time is almost every day. I do not believe that is in the best interest of the children.''