With my kids at those ages, I'd take them out in the MORNING.
Thus, once we got home for lunch, AT home, from any outings... their physicality was expended. And they got their yah-yah's out. Hence, after lunch, I kept things QUIET, and then it was nap time.
My kids napped for 2 hours too.
They were regular nappers and ONLY would nap at home. Not on the road. They were not portable nappers.
Hence I always scheduled things, per their naps. And did things in the morning. After all, kids wake up early in the morning and the day starts, early.
I even made *my* morning errands, into an "outing." We'd get breakfast, stroll around, go to a park, and back home. Sometimes, that is all we did and it was fine.
NO, I would NOT push back their nap times.
Keep them... on schedule.
If you tweak their nap times, it is often regretted.
And getting them back to a nap routine, is hard!
DO things in the mornings. That's what I did. And we'd come home, with enough of a leeway, that we did not have to RUSH through lunch. I allowed enough time, to get home, so that we could eat, unwind AND deflate.... BY NAP TIME.
This is important. Allowing enough time, so that lunch/their naps are not all rushed when you get home.
I had our routines, down pat. And it worked.
By doing this, my kids still napped as usual, at their usual afternoon times, after lunch and after the morning outing.
And it worked.
I rather do that, than to have had my kids get all fussy and overtired and their naps... delayed. Because, once my kids were over-tired... it made it MUCH harder, for them to nap and unwind. Getting kids too tired, backfired.
I knew the limits of my kids. We had outings and they expended energy... but I didn't get them OVER, tired. Just enough. Then home, lunch, unwind and nap.
After nap then it was hanging out and me cooking dinner etc. and mellow stuff. Their own play and imaginations.
Yep, in the car, have a small ice chest. Sippy's with water etc. simple non-perishable snacks. Extra clothes and footwear in the car. Band-aids etc., a First Aid kit in the trunk. Extra diapers and underwear too.
And the stroller. And a bag with stuff in it too as you go about.
When I had my 2nd child... naps or outings, were per the younger child's timing. Although, BOTH my kids napped, and I had them on the same nap schedule timing. So it worked out.
The other alternative you have, is to have the outings in the afternoon after their naps. But then, it would be too late... dinner has to be made etc. too.
For me, doing everything in the morning, really worked out best.
My kids woke up in the morning early, like about 6-6:30am.
And by lunch time, they were TIRED.