The celebrity interior designer wept uncontrollably and refused to leave her husband's side after identical charges against her were withdrawn.
The admission of guilt means the couple now face a potential civil damages action.
Ryder Richardson, 48, had been due to stand trial yesterday morning at Swansea Crown Court with her husband, Glasgow restaurateur Colin MacDougall, 46.
Gruff Davies-Hughes suffered serious head injuries at the Manor House Wildlife Park in St Florence, west Wales, when a heavy branch fell on him during strong winds in August 2010.
The three-year-old, who had been visiting the wallaby enclosure, spent three days fighting for his life in intensive care after being airlifted to hospital.
His mother, Emma, from Llanelli, suffered head injuries and fractures to her leg, pelvis and arm.
Richardson and MacDougall, who had moved from their home in Glasgow to run the park, had previously denied the charges against them and were ready to refute the accusations over the trial's scheduled three weeks.
MacDougall admitted the charges he had previously denied when they were re-read to him in the dock yesterday.
Ryder Richardson collapsed into his arms as he pled guilty to the offences. She then buried her head in her husband's chest and sobbed.
MacDougall also pled guilty to two identical charges on behalf of their joint company, Manor House Wildlife Park Ltd.
The two charges against Ryder Richardson were withdrawn, and she was told she could leave the dock while discussions about sentencing her husband continued. However, she clung to her husband's arm and, in tears, asked: "Can I stay?"
She was allowed to do so by the judge.
MacDougall is likely to be sentenced later this month.
The prosecution was due to be brought by Pembrokeshire County Council.
David Morgan, for the council, told the judge following the guilty pleas there was careful consideration before the charges against Ryder Richardson were withdrawn.
Mr Morgan said it had been clear she had little to do with the aspect of the company for which her husband was responsible. Ben Compton, for Ryder Richardson, added: "There was no evidence at all to link Mrs Ryder Richardson with any form of tree management whatever at this wildlife park."
Ryder Richardson and her husband clung to each other in obvious grief as they listened to the legal debate around them.
Mr Compton told the judge: "It has been a long two years for her, and your honour will see the effect on both defendants in the dock." Judge Paul Thomas released MacDougall on unconditional bail.
Mother-of-two Ryder Richardson made her name alongside Laurence Llewelyn-Bowen on the BBC's popular makeover programme Changing Rooms.
She moved to Glasgow after meeting MacDougall in his city restaurant and bar, Air Organic, and they married in March 2005.
In 2008 she gave up her TV career and bought the dilapidated 52-acre zoo-cum-wildlife park with her husband. She made the video diary- turned TV programme Trouble at the Zoo, which followed the progress of the site's redevelopment.
Ryder Richardson and MacDougall declined to comment as they left the court.