A three-hour ride from Tokyo Station, Mother Farm is a good place to visit if you want a relaxed day trip where you can be surrounded by lush greenery and adorable animals. The farm caters to both adults and children with various events and attractions such as fruit picking, animal feeding, cow milking, jam making, etc. A small amusement park for kids is also available on site.
JR offers a round-trip ticket including lunch for as low as ¥5500 for adults and ¥3500 for children. (Prices vary according to date.) The train leaves from Tokyo Station via the Sobu Line Rapid Service. The ticket is for the green cart, with no seat reservation. You then get off at Kimitsu Station, and from there you can take the highway bus, or the free shuttle to Mother Farm, which operates at fixed times.
For more information, check the English website.