Not generally needed. Multivitamins for children are not generally needed unless the child has the following (according to the mayo clinic): has an eating disorder has been diagnosed with failure to thrive doesn't eat regular or well-balanced meals doesn't get enough vitamin d through diet or sunlight exposure has certain chronic diseases or food allergies has a restrictive diet, such as a strict vegan diet.
Any. Any over the counter children's multivitamin is fine. If you chooses gummy vitamins make sure the child brushes his/her teeth after chewing the vitamin (to prevent cavities). Also be sure to read the bottle for dosing instructions. For 2 year olds, some vitamins are given every other day or a half tablet daily.