Children under the age of 3 can enter Walt Disney World for free and do not require a ticket or theme park reservation. Children aged 3-9 require a ticket, and the prices for these tickets range from $185 to $239 for a single day. Children aged 10 and above pay the adult ticket price. It is important to note that for entry, both a valid ticket and a date-specific theme park reservation via the Disney Park Pass system are required.