The Toronto Star, in its Parent Central pages, provided a lot of suggested ideas for family day activities. Some of the suggestions The Star has made are reproduced below. You can link to their site here: 
http://www.parentcentral.ca/parent/article/1132034--family-day-2012-39-fun-things-to-do-with-your-family  

The ROM: Learn about chocolate at Maya: Secrets of their Ancient, where kids can take part in Maya themed crafts, chocolate and tortilla workshops and more. Feb. 18 to 20, 100 Queen’s Park, 11 am to 4 pm, included with admission, 416-586-8000, www.rom.on.ca.
 
The TIFF Bell Lightbox: Attend a weekend of free celebrations including special family programming and workshops. Feb. 18 to 20, 350 King St W, free admission, 416-599-TIFF,  http://www.tribute.ca/showtimes/theatre/tiff-bell-lightbox/tiff/

 The Ontario Science Centre: Family Weekend programming will be focused on the Science of Flight, including hands-on workshops to create working parachutes, kites and paper airplanes, live flight demonstrations with a variety of bird species presented by The Canadian Raptor Conservancy and more. Feb. 18 to 20, 770 Don Mills Road, included with admission, 416-696-1000, http://www.ontariosciencecentre.ca.
 
Toronto’s Downsview Park: Family Day Fest will offer an indoor amusement park, featuring indoor rides, games, clowns, The Trevor Show and more. Feb. 18 to 20, 10 am to 6 pm, Studio 3 - 35 Carl Hall Road, Day Pass: $25 ages 2+ (incl. entrance + rides). VIP Day Pass: $40 (incl. entrance, rides, 1 temporary tattoo, 1 sticker book, 1 free carnival game play, 1 popcorn, & 1 cotton candy), Adults 18+: $8 (entrance only & accompany), VIP Family Pass: $96 (incl. entrance 2 Adults & 2 Children’s VIP Day Passes all inclusive), 1-800-567-3889,     www.familydayfest.ca
 
The Toronto Zoo: Celebrate the Family Day Weekend by visiting some of the Zoo’s featured families such as the Western lowland gorillas, orangutans, Komodo dragons and green tree pythons. Feb. 18 to 20, 361A Old Finch Avenue, 9:30 am to 4:30 am, included with admission,416-392-5929,    www.torontozoo.com
 
NFB Mediatheque: Drop in any time for screenings and pixilation activities at the Family Staycation Program; Feb. 18 to 20, 150 John Street, workshops at 10 AM, 12:30 PM and 3PM, free, but registration is recommended for hands-on workshops, 416-973-3012,   www.onf-nfb.gc.ca/eng/mediatheque/

CN Tower: Save 25 per cent off your CN Tower admission tickets all weekend long. Feb. 18 to 20, 301 Front St. West, discount tickets must be purchased on site, cannot be combined with other offers and can not be applied to CityPass and Premier tickets, 416-868-6937,   www.cntower.ca

The Second City Mainstage: The Second City Goes BOOM! is an hour of non-stop comedy and games that is suitable for all ages. Feb. 18 & 19, 51 Mercer Street, 12 pm & Feb. 20, 12 pm & 2pm, Tickets: $14 + tax, Family 4-Packs: $45 + tax, 416-343-0011,  www.secondcity.com
 
The Young People’s Theatre: The Great Mountain is the retelling of the Aboriginal story of Jumping Mouse, a young girl who discovers the transformative power of nature and the importance of courage. Feb. 18 to 20, 165 Front Street East, 2 pm, Tickets $10 to $20, 416-862-2222,   www.youngpeoplestheatre.ca
 
The Panasonic Theatre: Potted Potter, The Unauthorized Harry Experience - A Parody: by Dan and Jeff, condenses all seven Harry Potter books into seventy minutes. Feb 18, 3 pm & 7 pm, Feb. 19, 2:30 pm & 5 pm & Feb. 20, 2 pm & 5 pm, 651 Yonge Street, Tickets - $69.75, $39.75, $29.75, Premium seats $99.75 Includes Souvenir Program, 416-872-1212,   www.mirvish.com/shows/pottedpotter
 
Solar Stage Children’s Theatre: The Dufflebag Theatre Company’s presentation of Robin Hood, is an interactive play designed to delight kids ages 4 and up. Feb. 18 & 19, , 4950 Yonge Street, The Madison Theatre, 11 am & 2 pm, Tickets - $14, 416-368-8031,    www.solarstage.on.ca
 
Family Fishing Weekend: Ontario residents can enjoy the fun of fishing without a license this weekend. Feb. 18 to 20, event locations available online,   www.familyfishingweekend.com
 
The Kingsway BIA: Enjoy Family Day fun featuring ice sculpture carving and maple taffy demonstrations, arts and crafts, music and more. Feb. 18, 11 am to 3 pm, Willingdon Boulevard and Wendover Road at Bloor St. W., free admission, 416-239-8243,     www.kingswaybia.ca
 
Harbourfront Centre: HarbourKIDS: SK8 presented by RBC Play Hockey, will explore all forms of skating and winter culture from a kid’s perspective. Feb. 19 to 20, 235 Queen’s Quay West, 11 am to 5 pm, free admission, 416-973-4000,    www.harbourfrontcentre.com
 
Eight authentic Toronto heritage sites: Discover hands-on activities, historic cooking, old-fashioned games and crafts for kids at the Scarborough Historical Museum, Fort York National Historic Site, Spadina Museum, Todmorden Mills, Colborne Lodge, Mackenzie House, Montgomery’s Inn and Gibson House. Feb. 19 & 20, Pay-what-you-can,       www.toronto.ca/fundays
 
The Art Gallery of Ontario (AGO): Attend a family-friendly art-making extravaganza culminating in the creation of a day-long exhibition by kids titled Kid Nouveau. Feb. 20, 317 Dundas Street West, Family Pass 20 % off at $39 for two adults and up to five youths (ages 6 to 17), Kids 5 and under are free, 416-979-6648,    www.ago.net/family-day-2012
 
Casa Loma: Make reservations for a Valentine’s Family Brunch. Feb. 19, 1 Austin Terrace, Bookings accepted for seatings at 10:30am, 11am, 12:30pm, and 1pm. Adults - $51.45 + taxes, Children (4-12) - $26.45 + taxes, Children (1-3) - $13.45 + taxes, Children (under 1) - free, 647-725-1833 or 647-725-1832,       www.casaloma.org
 
Casa Loma: Participate in a hands-on Archery Workshop catering to children (ages 9 and up) and their parents. Feb. 20, 9:30am-11:30am, 12:00 noon-2:00pm, 2:30pm-4:30pm. Pre-registration suggested based on limited availability, $34.00 + HST/person.
 
The Hockey Hall of Fame: Kids will enjoy free entrance on Family Day. Feb. 20, 10 Front Street West, 10 am to 5 pm, up to a maximum of 4 youth (13yrs & under) will be admitted FREE with the purchase of one regular price adult admission, 416-360-7765,    www.hhof.com
 
The Drake Underground: Children’s entertainers The Monkey Bunch will be performing for people who love music, comedy and the planet, and really want their kids to love it too. Feb. 20, 1150 Queen Street West, Doors open: 2:30pm, Showtime: 3:00pm, 8.00 per monkey or $28.00 for a 4 pack,     www.themonkeybunch.com
 
The High Park Nature Centre: Participate in a drop-in Family Day Birds Program where families can make a bird feeder, learn about winter bird adaptations, borrow some binoculars, find out the best place to hand-feed birds, go on a self-guided hike, and help contribute to the Great Backyard Bird Count. Feb. 20, 440 Parkside Drive, 10 am to Noon, $2 recommended donation,416-392-1748 x 2,     www.highparknaturecentre.com
 
Piola Restaurant: Piola’s pizza makers will show kids 14 and under how to stretch out the dough, roll it, and then pick out their favourite toppings including house made tomato sauce and as much cheese as the pie can hold. Feb. 20, 1165 Queen St. West, 11:30 am a.m. to 3:30 p.m., accepting advance reservations, pizzas are $10 each and include a pop or juice (limit one pizza per person), 416-477-4652,       www.piola.it