The three on this page are chosen for exactly that: simanim cards for each seat at the table, a tzedakah box to decorate and then fill, and an air-dry clay honey dish. Each is one sitting, and each ends with something that goes on the table on yom tov — which is most of why children stay with it.
The simanim cards work from about five upward, with an adult handling the gold pen. The tzedakah box suits roughly six and up. The clay honey dish is the most forgiving of the three and younger children manage it fine, since imperfect pinch pots look intentional once they are painted.
Give the clay a week. Air-dry clay needs a day or more to harden fully before it can be painted, and paint needs its own drying time on top. The cards and the tzedakah box can both be done the week of, or even the day before.