Activity and exercise are an important part of a baby's development. Gentle movements in a lateral motion are fine to avoid any stomach acids bubbling upwards. Anything other than this type of activity may cause more discomfort.
A baby excited to see their older sibling come in from school cannot be stopped from waving their arms and legs about excitedly and laughing/pointing and it's very important to you to have found a moment of joy. Don't be too quick to stop all this activity. Try to limit playtimes to an hour after feed times and avoid lying baby
flat to play under a gym or lifting baby in an 'up and down' type
manner.
In addition for toddlers suffering with reflux, exercise can cause the blood supply working around the digestive system to relocate to support muscles groups away from the stomach, thus causing food to stay in the stomach for longer and the potential for acid to build up is greater. The activity itself may also cause the contents of the stomach to splosh around which is why its important to give small meals before an activity.