The train can get very crowded at certain times- Sunday evenings are terrible. I would recommend the bus. These are very regular. Look up times and stops for both the Oxford Tube and X90- different companies. Do not drive- you will not be able to park
The botanical gardens are lovely. The Ashmolean and the Pitt Rivers are great. Go to Magdalen College and walk along the river
Train. The Natural History museum is closed right now, being refurbished, the Pitt Rivers is still open though. The Ashmolean is always nice, they usually have family activities on weekends. If it's sunny, G&D's for an ice cream and maybe a walk through Christ Church meadow down to the river? The botanical gardens are also nice for walking around.
Definitely the train. Parking is awful, and you are strongly advised to use the park and ride, which means a longish bus journey in. The station is much closer. I always recommend the Pitt Rivers and University Museum, the University Parks are very close, and good for running about in.
It is quick & easy on the train from London: that would be my preference. A lot of the centre is one way street/pedestrianised - I wouldn't personally consider a car useful there assuming you want to go to the museum, colleges, meadows etc.
Two couples are planning to take our kids to Oxford from London (10 month old twins and 9 month old boy with his 3 year old sister). Any advice on best way to travel (train v. cars)? Any thoughts on visiting the city with this group...what will be challenging with strollers? what activities will work for us v. not? what things would be especially good to try and see/do? Any pros/cons or things to consider before going would be super helpful. Thanks,