The 38-year-old woman and two children are said to be in a serious but stable condition following the “isolated incident” in Hunters Way in Uckfield on Thursday morning.
Sussex Police say there is no threat to the wide community - but people living in the local area have told The Independent of their concerns.
A force spokesperson said: “While their conditions remain serious, they are currently in a stable state. A woman has been arrested on suspicion of administering a noxious substance / poison to cause injury.
“We are not searching for anyone else in relation to this investigation.
“Our enquiries are ongoing and a heightened police presence is anticipated in the area at this time. This is being treated as an isolated incident with no threat to the wider community.”
The incident has shocked the local community.
Uckfield is town in east Sussex with a poulation of around 15,000 people which sites between Brighton, Eastbourne and Tunbridge Wells. Hunters Way is an estate of large detached homes in a north west area of the town. House prices were an average £375,000 last year, according to Rightmove.
Dan Manvell, councillor for the town’s north ward, told The Independent: “It is obviously something which doesn’t usually happen in Uckfield. Nothing more than low level antisocial behaviour occurs here, so this is worrying.
“It looks like an isolated incident but I’m sure it is upsetting for all those involved, including the family. I hope they get better soon.”
Rob Birchmore, aged 51, owns a flooring business on Hunters Way. He told The Independent he heard about the incident through a post on Facebook by the local policing team.
He said: “As soon as I heard I checked on my wife and my family - yes, it is worrying. Nothing like this has happened before. We’ve had a few thefts from traders on the road, but nothing like this.
“There are many young families and elderly residents on the road. The police really need to come down and speak to everyone to reassure people living here, as this is not normal and people are concerned about their safety.”
On Facebook, Lucy Hawkes said: “Oh those poor kids I hope they all make a speedy recovery.” And Val Frost wrote: “Hope all will be ok. Shocked how close this has happened.”
A spokesperson for South East Coast Ambulance Service said they did not comment on call-outs to private addresses.