The Milwaukee County Sheriff's Office said they are investigating an alleged sexual assault that happened at Humboldt Park Pavilion in Bay View Sunday.
Neighbors said a man assaulted a child in the nearby bathroom.
"Who would do that and violate our safety and violate our trust of our beautiful park and feeling safe here," said Rebecca Milaeger, a parent.
"It's definitely frightening," said Rudi Heinrich, another parent.
"Just shock and it's a little scary, a little disappointing that that happens at a children's playground in the middle of the day with tons of adults around," said Chrissie Pappas, a parent.
Witnesses said a family was at the park Sunday, next to the beer garden when their 4-year-old used the restroom. Parents said the boy's mom went to check on her son and apparently found a man in the stall with him.
"I thought how many times have I let my children run around this park and I wasn't watching them every second," said Milaeger.
"Kids deserve to have to learn independence when they're sort of young and it's right there," said Pappas.
The Sheriff's Office said they have a suspect in custody. Neighbors believe the man was someone at the beer garden.
"It does make me remember to be vigilant and watch my daughter," said Pappas.
"Reminding myself to be aware of what my children are doing and how long they've been gone," said Milaeger.
Neighbors aren't letting the alleged incident stop them from going to the park.
"We love the park. It's a big part of why we're in this neighborhood and we wouldn't let an isolated incident like deter us from us enjoying ourselves here," said Heinrich.
The Sheriff's Office said charges are expected later this week.