"We'll start with a walk and work out way onto other things." Toriel can see how overwhelmed her son is in the moment, starting small is for the best.

"I believe there are vendors around here, so we could have lunch?" She would offer to cook, but Toriel doesn't want Asriel stuck inside, she wants her son to experience as much as he can of the surface. Human and monster vendors alike have found places amongst the park, amongst the people enjoying the weather. It isn't technically legal, but monsters are in a gray area at the moment.

Toriel is willing to overlook many a thing now to ensure her son has a good day with her. Given some time she might find Asgore, see if Asriel wants to see Asgore. For now, she brushes away the thought.