Children with pus filled gums can be caused by gingivitis, or apical periodontitis. 1. Gingivitis: Gingivitis can be caused when the gums are stimulated by calculus or plaque. After repeated stimulation by inflammation, children’s gums may grow pus and may be accompanied by pain. 2. Periapical periodontitis: When the pulp of a child’s teeth is damaged, it can cause periapical periodontitis, which can also lead to pus in the gums and may be accompanied by severe pain. 3. Trauma: Trauma can also lead to abscessed gums if the infection is not controlled. Children with pus filled gums can also be caused by periodontal abscesses and other causes, should be promptly to the hospital for treatment.