Can both children participate meaningfully?
Watch whether one player makes most decisions while the other follows. A simple supporting role can be enjoyable, but ask the child in that role whether it feels like playing. Check whether the game requires quick simultaneous actions, independent reading, or accurate movement. Those demands may matter more than the characters on the box. If a child needs help, explore available accessibility or difficulty settings in the current version rather than assuming the default is the only way to play.
What happens when someone makes a mistake?
Try an ordinary failure and see whether the whole team must restart, one player can recover, or the game continues. Talk about the result before frustration builds. Agree that helping means explaining or demonstrating when invited, not grabbing the other controller. If the game repeatedly puts one child in the position of delaying everyone, choose a different arrangement. Shared play does not require siblings to accept a role that consistently feels unfair.
How long should the first session be?
Choose a natural stopping point that leaves time to discuss the experience. Ask each child separately what they enjoyed and what was difficult. One may want more challenge while the other needs a slower mode, and both observations are useful. Consider alternating who selects the next activity. The successful choice is the game your actual group wants to return to, not the one that sounds most cooperative in a description or has the most impressive review score.