The recommendation every time would be to invest in a real piano, especially for kids. Mechanical and electric keyboards are two very different things. The keys respond differently - mechanical keys cause strings to be hit with a padded hammer and have a wide dynamic range; electric piano keys cause an electronic circuit to be closed which produces the sound, with no to just moderate dynamic range. The more expensive electric pianos have built in touch sensitivity and weighted keys which try to emulate a real piano, but it is not the same, and you will reach a point where you might as well buy a decent second hand piano. Only a real piano can help train your fingers to learn the fine motor skills and strength needed to play a wide repertoire of music, classic and contemporary. Electric pianos and synthesizers can wait until a later time.