Police are searching for a man who was spotted kicking a child near Worthing seafront.
He was seen shaking a child aged between one year and 15 months near The Lido at about 10.25am on Friday.
The toddler was dropped to the floor and kicked.
Witnesses said the man left with a child in a buggy and was last seen heading towards Montague Street.
A spokesman for Sussex Police said: "An extensive search of the area was made by a number of officers, utilising the Shopwatch system and CCTV, but were unable to find the pair.
"Police are extremely concerned regarding this welfare of the child and need to locate the man involved as a matter of urgency."
The man was described as white, about 5ft 8in, aged between 40 and 42, with short grey hair.
He was wearing a red jacket with black on both sides and a black hood, black trousers and black trainers.
The child was wearing a hat and was in a dark blue buggy.
Anyone with information is asked to call Sussex Police on 0845 6070999 quoting serial 796 of December 18.
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