Can someone help me with a reality check?

My husband and I are taking our 22 month old toddler to my husbands grandmas 90th birthday party in their city today. I’m in my 3rd trimester pregnant and I’m doing fine but it’s kind of rough in this heat wave. Their city is a 3 hour drive away and we’re getting there early just to make sure we’re not late. We will have 2-3 hours to spend before the party. It will be 86 degrees and there’s an air quality alert for pollution and heat advisory.

My in laws want to take my son to the playground to play for that time. I think it’s too hot and dirty outside for that and want to just stay inside. We usually spend a ton of time outside but this is extreme weather for our area. Would you let them do that? Also, would you feel safe or comfortable walking 20 minutes outside in the city to a restaurant? The other option is for my husband to drop us off and walk by himself.