That is a correct sentence, but "être en train de" is only used when you really want to emphasise that the action is taking place at this moment. Otherwise, simple and continuous are both expressed with simple in French.
Not wrong, but only to be used if you really need the emphasis that this is going on right now (at the time of speaking).
Does "petit garcon" imply the boy is very young, as it would in English, or is it size description?
Same as english. It could mean little as in short or little as in young
This is a sexiest statement. Shame on you!!!