4-year-olds are a little better at posing directions but are still very young that they may not understand everything you are trying to say. But often times they will give you their best interpretation of what you are trying to get them to do and often times that is a much better pose because it catches their personality with it. So don’t get so hung up on getting the pose correct when you can get the solid gold of a pose that catches who they are even better then the pose you had in mind.
One other thing, that I will likely reiterate or at least repeat on the next post: clothing. Keep it simple. Either patterns or solid colors or a mix of patterns and solid colors but you don’t want complicated designs. Simple colors or simple patterns look great in photos. That shirt you have that has that long winded speech on it is just going to end up distracting everyone as they try to read your shirt.