An eyewitness tells ET the two actively helped Maceo decorate a pumpkin. At one point, Martinez put his hand on Berry's shoulder, and they both seemed very comfortable.
Another eyewitness says that the two were "close with one another" at the event, and smiled a lot while they "doted over Maceo, looking like happy parents."
"He was carrying her bag and was gentle and loving," the source continues. "At one point he put his hand on her shoulder, never would have thought there was trouble. They stayed at the party for about two hours."
There were a few other celebrity sightings at the fair, including Modern Family's Ariel Winter and Julie Bowen, as well as Channing and Jenna Dewan Tatum. Channing even posted a picture from the event, writing, "Pretty sure I terrified all the children at our daughter's Halloween carnival today. Btw- I'm pooh bear in case anyone can't tell."
This is Berry's third divorce. The actress was married to baseball player David Justice and singer Eric Benet, and dated model Gabriel Aubry, with whom she has one daughter, 7-year-old Nahla. Split rumors began to spread for the former couple when Berry was spotted without her wedding ring in August. The two have been married since July 13, 2013, and have one child together.
The last red carpet appearance the exes made together was in February at the Treats! Magazine Oscars party.
A joint statement sent to ET on Tuesday by reps for both Berry and Martinez reads, "It is with a heavy heart that we have come to the decision to divorce. We move forward with love and respect for one another and the shared focus of what is best for our son. We wish each other nothing but happiness in life and we hope that you respect our and, most importantly, our children's privacy as we go through this difficult period."
Meanwhile, last week, Berry and Martinez were hit with a $5 million lawsuit over an alleged incident with an LAX employee that happened on Jan. 4. Ronaldo Owens claims that Martinez "brutally and intentionally charged at him using an empty child's car sear he held in his hands as a weapon, striking [him] to the ground with the seat, and causing [him] humiliation and injury." At the time, Owens says he was in a designated area in the corridor that Martinez and Berry were being escorted down that is used for high profile passengers, and was trying to take video and photos of them along with other employees.
When ET last caught up with Berry at Comic-Con in July, all her focus was on her show, Extant.