It was one of three incidents dealt with by the Coastguard and the RNLI since Friday, following a yacht's mayday call and reports of a kitesurfer in difficulty.
The Selsey Coastguard Rescue Team said it was sent to West Wittering Beach shortly after 2pm.
"The child was found by a member of the public and we reunited the child with the family," a spokesperson said.
"As we reunited that child with their parents another missing child had been reported missing but as we were taking further details the child was located safe and well."
The team was stood down to continue with its safety patrol.
On Friday evening, just before 6.30pm, the Coastguard team was paged to reports of a kitesurfer in difficulty off Bracklesham Bay.
"On arrival the casualty was making good progress back, and made it safely back ashore.
"The team made sure the casualty was alright, no medical assistance was needed, after they got in to difficulties out at sea."
The Coastguard reiterated its ongoing warning to people when near the sea.
“The coast and the sea can catch you out whether you’re local or not," it said. "Our message remains: call 999 Coastguard if you’re in trouble. Please help us and our families to stay safe. Be aware of the risks, and keep your distance.
"In an emergency out at sea, on the beach or along the coast dial and ask for the Coastguard."
These incidents followed a mayday call from a small yacht in Selsey on Friday morning.
"The UK Coastguard received the mayday from the yachts skipper who was concerned the sea conditions would overwhelm his yacht," an RNLI Selsey spokesman said.
The Selsey All-weather lifeboat (ALB) was launched just after 11.10am and 'initially headed straight out from the beach', as the lone sailor 'had not confirmed his position'.
Communication problems resulted in the ALB not being able to use the direction-finding equipment.
The casualty eventually reported that he was between Selsey Bill and Wittering.
The spokesman added: "After passing the Bill, communications got better and eventually the ALB was able to get a bearing off the yachts radio signal and headed towards a radar target on a similar bearing.
"Both the ALB and the rescue helicopter, which had also been scrambled, arrived on scene at 11.37am. After speaking to the lone sailor about his welfare the lifeboat coxswain reported to the coastguards that the helicopter was not required."
The lifeboat transferred a crewman to the vessel to assist the skipper with lowering the sails and clearing the decks of ropes before starting the engine and escorting the casualty vessel to Chichester Harbour/
At 11.50am, the yacht was underway with the lifeboat crewman on the helm following the lifeboat towards Chichester harbour.
The yacht was safely berthed alongside at 1.20pm and the ALB was released from the incident at 1.30pm.