Background: Mobile Internet-connected electronic devices provide access to activities that have traditionally been associated with sedentary behavior. Because they are portable, these devices can be utilized in any environment. Therefore, providing children with access to these devices in environments that typically promote physical activity may result in a reduction in physical activity behavior. Purpose: To assess children’s physical and sedentary (ie, sitting) activity with and without the presence of a mobile Internet-connected tablet computer. Methods: A total of 20 children [6.7 (1.9) y old] participated in 2 simulated recess conditions in a gymnasium on separate days. During each condition, children had free-choice access physical activity options and a table of sedentary activities for 40 minutes. During 1 session, the iPad was present, and in the other session, it was not. Physical activity was monitored via an accelerometer, and sedentary time was monitored via a stopwatch. Results: Children significantly (P ≤ .03) reduced average physical activity intensity and increased their sedentary behavior with the iPad present [4.4 (4.0) metabolic equivalents/min and 20.9 (12.4) min sitting] versus the condition without the iPad present [5.3 (4.0) metabolic equivalents/min and 13.6 (13.2) min sitting]. Conclusion: Introducing an mobile Internet-connected tablet computer into a gymnasium reduced children’s physical activity intensity by 17% and increased sedentary behavior by 54%.