Inspector Richard Quinn, from Cumbria Police said:
"The dog is currently in our care. Because a child is involved we need the full facts before we can determine what should be done with it.
"At this stage we haven't had an opportunity to interview the parents but we believe this may have been a terrible accident."
More top news
Sandy Murray, of Police Scotland, was was giving evidence at the trial of a bus driver who denies killing Ryan Baird by dangerous driving.
34-year-old Christopher Peck was involved in a head-on crash with a drunk driver. His funeral has taken place in his hometown, Workington.
The arrests come weeks after a much-publicised series of appeals to mark the 30th anniversary of the 18-year-old's death.