Toronto is well-served by international and domestic flights to its main airport. There are a few more options if arriving from the USA, including a smaller island airport and a couple of Amtrak trains from Buffalo and New York. You can make a land crossing into Ontario from the southwest at Detroit-Windsor.
The best price found from United States to Toronto is on June 29th, 2019, travelling with American Airlines. See more options, compare prices and book: search flights.
Toronto is a kid-friendly city: there are plenty of things to see and do when traveling with little ones in tow.