The way we teach our kids is to swing your knee up to the side first, flick the kick, keep your alance with your arms out and bring the knww back to the same position. Only then do you drop back into zenkutsi (yes i know its spelt wrong) dachi. It probably depends on the style of karate too. As bushido man says he does the roundhouse kick then lands forward, our style we practise against a pad dropping backwards.