I suggest whatever 16% protein sow & weaner pellets you can get cheapest. Rhubarb and potato are poisonous. Don't give too much greenery at once - it can become impacted in the gut of young pigs. If you give grain of any sort soak it first - feeding it dry can cause prolapse of the anus. A handful of good hay, apple tree leaves, bolted lettuces, woody carrots and parsnips all go down well and will keep them interested and happy. We have large concrete pens but floor feed over a wide (clean) area to keep them busy rooting about. Cut apples in half before feeding - growers can choke on whole ones.