It's helpful to buy tickets online, in advance. The price is the same but you can skip any entrance lines. The special exhibit is always extra, but can be purchased online as well. Depending on the ages of your children these exhibits are generally worth it.
It is a busy museum either during holidays or with school groups during the school year. But it is large enough that you generally don't feel cramped. It's best if you can go in opposite direction of the school groups, start at the top and work your way down and rest and snack before or after traditional lunch time.
The Royal Ontario Museum (ROM) is open every day except December 25th.
Wondering what to do in Toronto with kids? Spend a family-friendly day at Toronto’s Royal Ontario Museum (ROM) and combine it with a mini-adventure on the subway . Your children will enjoy the thrill of taking the metro and the growing excitement as you gradually approach your destination. Engage your nuggets en route and teach them how to follow a subway map. Upon arrival, explore ROM’s dark and eerie bat cave. Visit an Egyptian pyramid and see what a real mummy looks like. Watch your children as they dig for dinosaurs and try on a knight’s armor in the museum’s hands-on exhibits. Finally, take in one of ROM’s amazing special exhibitions.