Hi, the bottle is a part of his bed time settling routine and is acting a bit like a dummy to send him off to sleep. The real question is how much do you want him to stop using it? If you're not that bothered then don't try as you'll only give in and then it will be much harder the next time. There are of course issues around teeth etc.
There are 2 approaches I have used in the past, the first is a step by step approach, the second more cold turkey though dressed up nicely.
- Separate the milk in the bottle from actual bed time, do your usual bedtime routine put him in his PJs give him his milk and a cuddle out of bed, maybe with his story then put him to bed with the empty bottle. 2-3 days later or so do the same but take the bottle away once he is settled in bed. 2-3 days later take the bottle before he lies down, then 2-3 days after that take the bottle before cleaning teeth and settling, after a week or so of this buy a new "special cup" for night with him and immediately throw all the bottles and teats away ( cut them if you'll be tempted to get them out of the bin). Give him his new night time cup before teeth cleaning and bed but don't leave it in the room with him. Long drawn out but gentle!
- Talk to DS about how grown up he is say when you were a baby you used to....now you do this....., find a few examples ( walking, riding trike, eating food etc.) say "now you are a big boy it's time for the bottle fairies to have your night time bottle and to leave a present for a big boy" Make a big deal of putting the bottles etc in a nice gift bag last thing at night and hanging it somewhere visible but not accessible. Put son to bed and Immediately get rid of all bottles teats etc. (make sure they are irretrievable and completely gone or either he will find them or you'll be tempted!) put a suitable present in the bag could be a cup or a toy or anything that you know will surprise and delight him). Put the bag back. First thing in the morning take him to the bag and give it to him to open.
Either will work but only if you are sure that you want to do it. If you are too tired or not really that bothered leave it until you really really want him to give up the bottle or you won't be able to follow through. ( we've all been there!!!)
Best wishes