These are all informal British terms to refer to a man or boy. 'Lad' is equivalent to 'boy'. It suggests someone fairly young. A male child or even a baby can be described as a lad or little lad. Teenagers can be lads. An older person might describe someone in their early twenties as being a 'lad'. In recent years, the word has taken on added connotations. In British culture, the term 'lad' suggests a male in his late teens or twenties who enjoys socialising, drinking and possibly womanising. A lad enjoys life, but is somewhat immature. 'The lads' is a term used to describe a bunch of friends who socialise together. Their socialising may involve football and most certainly fair amount of alcohol. 'Bloke' and 'chap' are both slightly more old-fashioned terms. They often describe an ordinary man in the street. 'Bloke' tends to have more working-class associations, whereas 'chap' is rather more upper-class. This can apply to both the user and the person described. 'Bloke' is always an adult male, whereas 'little chap' can be used to refer to a child.

Not much. Lad tends to have the connotation of somebody younger, including boys. "My lad" our "lad" would mean son, but this again can refer to a man or a boy. Chap and bloke only refer to men. Chap and bloke are largely interchangeable. Chap has an additional usage as an informal way to address a friend or friends. For example I might greet someone with "Alright, chap?", but you could not use this phrase with bloke.