Married actors Rob Mcelhenney and Kaitlin Olson have been slapped with legal papers after their dog allegedly attacked a 19-month-old baby.

Plaintiff Julie DeLagarde claims her daughter's face was mauled by a German shepherd owned by the It's Always Sunny in Philadelphia co-stars while she attended a Father's Day party the couple threw in Los Angeles in 2012.

In her lawsuit, DeLagarde alleges the dog, which was not on a leash, bit the side of the toddler's face "without provocation", leaving part of her cheek "hanging off with all the insides of her face exposed and blood streaming everywhere".

She is demanding unspecified damages to cover the costs of additional plastic surgery procedures to prevent her child having to live with her scars for the rest of her life, reports Tmz.com.