My 3 year old just does ballet, though we are looking at starting her with swimming and we may look at gymnastics too, but after she starts primary school and we see how tired she is/ whether she is getting enough "down time".
When she goes to primary school she will probably add more in, but in reception year not much I would think. The school we are hoping she will get a place at has tons of lunchtime and afterschool activities including lots of different sports, music groups, art, drama, extra languages, chess etc, but a lot of these are not open to the infant classes, I think just football, tennis and "gardening club" for reception year. We will let her choose which of these she wants to do.