Not sure how often the younger kids play but my ds12 was on the ice 4-5 times a week with the team
Different programs will require different levels of commitment.
For example, our local rep program (where kids try out and have to "make" the team, based on skill levels) will involve the 4-5 sessions per week (practice, power skating, home game, away game) plus a number of tournaments throughout the year (most will be out of town and involve booking a hotel room, paying for meals and gas, etc.). Our local rep program starts at senior tyke (turning 7 by December 31st). There is usually also a fundraising component to any rep team. All rep kids pay the house league registration fee PLUS a rep surcharge, and will need to pay for team wear (usually a windsuit, hat, etc).
Our local house league (where every paying kid gets to play, and has equal ice time no matter what skill level you are at) will only have one practice and one game per week, and all at a local rink. There are no mandatory tournaments, though most teams choose to take part in the one hosted by the local association over the Christmas holidays. No team wear purchase required, and the only fee you need to pay is the one-time registration fee (though some associations do have their house league kids take part in fundraising to offset costs.....our centre, luckily, does not

).
Call or email your local minor hockey association to find out (a) the cost per child (sometimes you will get a family discount if there is more than one participant in the family) and (b) exactly what you get for that cost. Some centres provide jerseys to keep as well as team socks, others provide jerseys on loan and you must provide your own socks. They should be able to tell you when your child's age group will play (ie. game Saturday a.m. at either 7, 8 or 9 a.m. and practices Thursday evening at 5, 6 or 7 p.m.).
Keep in mind that fees will vary widely from centre to centre. For example, our city's minor hockey club charged $320 per player for house league for the 2008-2009 season (with a keeper jersey, year end trophy, 19 regular-season games, 12 practices, and play-offs for all participants). The neighbouring community (just 10 minutes to our west) was $100 more for a very similar program. And our neck of the province has it cheap, compared to some others. I have seen some house league registrations at over $500 a player. I have also seen another local community (to our north) with fees under $300.
Hockey can be a big committment. Check it all out and decide if its an adventure you want to embark on.

Its not for everyone (my sister and brother wouldn't enrol their kids in a hockey program to save their souls) but for other families, its a way of life!!