Agree with Anchovy, you need to be firm.
Bedtime is bedtime, it is not time for debates, time to eat dinner which they didn't finish earlier etc.
If they really can't sleep, then playing with a toy could be accepted, subject to them staying in bed... thus teddies/dolls are often best, though I know some boys who take a Thomas The Tank Engine train.
If your child is inclined to pester for a drink, then before leaving them to go to sleep, make sure they have a drink of water on their bedside table... suggest a non-spil cup.
Some children like to have a reassuring light on somewhere. Typically in that case, I would leave the door open or partly open, and have a bathroom light on.
To change the habbits of a persistant get-out-of-bedder, you need to remain within close approximity, so that you can return them to bed the instant they get out. At first, I'd suggest sitting just outside their bedroom door, out of view. Then as they get used to the idea, progress down the stairs, a few steps per night. It may take a week or so, to get all the way down, but when you do... problem solved.
Have a good bedtime routine, so there is a clear lead-up to bedtime. This would typically be toilet, teeth, choosing bedtime story/stories. Read bedtime stories - with child in their bed if possible, so once finished you can kiss them goodnight, turn out the light, and leave their room.