Britney Spears joined sick children for art therapy earlier this week.

The 'Piece of Me' hitmaker - who has children Sean Preston, eight, and Jayden James, seven, with ex-husband Kevin Federline - took part in a collage-making exercise with youngsters at Children's Hospital Los Angeles on Tuesday (11.03.14), and told the group she believes butterflies are her ''guardian angels''.

Working to the theme 'What it feels like to be away from home', the group sorted through magazines to and selected images that reminded them of home under the guidance of Art Therapist Nicole Albers.

Britney chose a photo of happy children to represent her boys, an image of a crawfish, which she said was her favourite food, and a butterfly.

She said: ''Butterflies are our guardian angels.''

The group decided to name their collective work 'Happiness' because when they think of family, that is how they feel.

After the therapy group, Britney spent time in the Heart Institute, the Medical/Surgical unit and the Children's Center for Cancer and Blood Diseases.

She later tweeted: ''@ChildrensLA I had the best time, thank you for having me!! xox.''