Considering your children are still pretty young, I would work with them helping them (unless it is something very easily done with one person) and I would also suggest a timer so that they know they have to work for a specific time and then they can return to their games, etc. If you leave it as "you're grounded until its done" it makes the chore seem unacheivable and easy to put off. A timer and working hard and fast for 15 minutes-knowing there is an end to the work seems more do-able. Then take a break and if you have another chore do the process again later.
Also, it is very important that they feel like they are doing something to help you and you make a point to show that you appreciate their help. Kids actually like helping when they are thanked or asked like, "hey, could you help me pick up? that way we can go to the park later..." type of thing.
When my kids got older I would still ask them nicely, but when I got, "Oh, mom..." then I would get tougher and say, "ok, you can either help me pick up the livingroom now, or I can find you a lot more things you can help me with". They would usually get busy so that I didn't find more chores for them to do. I'm not an expert, but this worked for me. Honestly, though --it is still a battle sometimes.
Now, my six year old loves helping me. I don't know how he got that way, but he will sometimes just clean real good and come get me and show me what he did. I always say, "wow, that is so awesome! I can't believe you did that all by yourself (even if he made the bed and it's all crooked or whatever!) and he is SO PROUD. I think that is the key. Make them feel like they are a needed part of a family and that the work they do helps you and the whole family. Tell them, this is what families do is help each other.
Also, try to make it as much fun as possible when you are working together. Be their "coach" and not the drill master. Be more like, "com'on guys, lets go, lets go..." instead of "if you don't start picking up those toys you are going to be grounded!". It changes the whole tone and it doesn't seem as much of a chore.
Hope this helps.