A 31-YEAR-old man chastised the children of a Redditch woman too severely, a judge was told.
The behaviour of Paul Arnold upset the victims' grandparents, who discovered bruises on their arms.
Prosecutor Paul Whitfield described how Arnold held a girl upside down by one leg and smacked her bottom.
She described the pain as "like a lot of wasps", Worcester Crown Court heard.
Mr Whitfield said Arnold used unreasonable force and was "a controlling figure".
Arnold, now living in Fivefields Road, Willenhall, pleaded guilty to five counts of child cruelty.
He was questioned by police after the NSPCC alerted social services.
Sir Andrew Watson, defending, said Arnold had used "inappropriate methods" but was overtired because of work.
He said the woman had made similar allegations against a previous boyfriend.
Judge Andrew Geddes adjourned sentence for the children's grandmother to give evidence after her statement to police was contested by the defence.
He ordered Arnold, a former long-distance lorry driver on the Continent, to keep away from Redditch except for visiting his parents in Hunt End.
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