What kind of activities a 4 month baby can do...

At 4 months your baby is just about learning to understand the world around, in terms of sight and sound. At this age, your baby will be very curious about various sounds and visuals. You still don't need a lot of toys at this age for your baby. Try simple games such as holding a rattle and moving it from side to side. Show it to your baby, keep it just near the grasp and then take it a little away. This will encourage your baby to look at the rattle and try to reach for it. You can also start reading simple board books now, showing various pictures to your baby and reading out the word loud.