At 3 weeks its better to keep them confined and let them get a little bigger before exploring. As far as eating solid foods, if they are nursing well and mom has plenty of milk, don't attempt to give solid foods till about 5 weeks old. They really will not be very interested in it and you'd only frustrate yourself (I've raised a lot of kittens)
When you start, make it a soupy mixture of canned kitten food and some KMR and hot water. I'd keep mom out of the room when teaching the kits how to eat or she will eat all of it. Then take each kitten and put some mixture on your fingers and let them lick it off; some take it right away, others will not want any parts of it and you might have to open their mouth and put some on the tongue a few times.
Once they start eating more, then you can line them up around a shallow plate or paper plate and push their face a little in the food - not too much tho
In about a week or so they should be eating on their own.
Keep the kittens and plate on a cleanable surface (like bath room tile or a cage as they WILL get messy and you may need to wipe off paws, etc. after every meal.