Trace the full route with the pushchair
Start at the arrival point and follow the planned route through entrance, ticket desk, activity, toilets and exit. Ask about steps, lift dimensions where relevant, narrow gates and whether the route changes during an event. The accessible entrance may be some distance from the entrance the group normally uses.
Ask what happens at the venue door
A venue may admit a pushchair to the building but ask visitors to leave it outside a particular exhibition or seating area. Ask where it can stay, whether the area is staffed, and how the accompanying adult can carry loose items or move onward without it. Let that adult judge what arrangement is workable.
Choose a fallback with honest limits
If the pushchair must be left outside a room, decide who will carry loose items and how the child will move through the next space. Choose a second route or different activity if the arrangement is not workable.
If a lift is temporarily out of service, check the return route as well as the way in. A downstairs entrance is of little use if the only exit passes through a level the pushchair cannot reach. Pick another route or activity rather than relying on unplanned lifting or assistance that nobody has agreed to provide.