My grandson who is 3 won't go out of the house unless he is wearing his fleece hoodie even in 27 degree heat any suggestions?
Some children with sensory processing or attachment issues have strange choices when it comes to clothing.
An example: I knew a child with profound sensory processing disorder who would never wear pants, not even if there was three feet of snow on the ground. Their parents gave up (wisely, imo) and let him be who he was/is. He did everything neurotypical kids do, including snow sports; he just did them wearing shorts. He even wore shorts at his wedding.
My suggestion is to show the child love and acceptance by respecting their choices if they harm no one. Let the child wear the hoodie making no fuss whatsoever (keeping the child well hydrated, though, is a good idea) unless they are actively harming themselves (red, profusely sweating, and unwilling to return to home.) If they get too warm, they will take off the hoodie and you can carry it, or endure the heat to the point that you think they need to go back home, which is a natural consequence of their choice.
Parents and grandparents often wish for a child to behave in a certain manner because they feel comfortable with a certain behavior. Clearly there are areas where this is important to implement, but wearing a hoodie when it's warm probably isn't one of them.
Issues like these, I find, rarely have a single simple answer, but the solution is usually something you'll tease out with a lot of experimentation. Some of the things we suggest here may be good general advice but simply miss the mark entirely in your specific situation.
It could be helpful to introduce play. "Yes! Let's put on really warm clothes because look, it's snowing outside" and then you go to a sandbox and try to build a sand-snowman; hat, carrot and all. "What's this? The snow is melting away. Not it's summer!" and then you run back inside and change into something too cold, instead, and go out and playact summer. Perhaps also run a third iteration matching the current weather, so the child isn't left with the impression of freezing when going out without the hoodie.
I'm not suggesting you should have time for this routine every time there's a conflict revolving around the fleece hoodie. This is intended as playful practice when you have time set aside to work on this issue; a playful introduction to the concept of dressing according to the weather, and a way to make the idea of going outside without the fleece hoodie less threatening. Using play in the heat of the moment may also be helpful to navigate a perceived threatening situation, but could perhaps be something less ambitious. If you've done the above, it could be as simple as referring back to that "Oh, yes, because it's winter again, right? Yes, I see now, it's snowing outside. No wait! It's summer!"
It could be that you'll need to hold a limit, and say "I'm sorry, the fleece hoodie is for cold days only", and stay with him through his entire upset, and hold a safe space for him to have all of his big feelings about this. Don't leave him to "cry it out", but stay close and validate his feelings. "I know, you really love this hoodie, and now it's too hot outside to wear it. I get it, that must be really hard." Sometimes, merely allowing the child to have their big feelings and trusting that they'll find resilience and work this through once they've had a chance to cry about it and really be heard, will be enough. Sometimes, your modelling and the safety you provide throughout this upset will encourage the child to talk about how they feel about the issue, and you may unearth reasons you'd never imagine for why the hoodie feels so important. Perhaps it's filling a need that could be filled another way, that the child hasn't seen.
We really have no way of knowing what's driving this particular need in this particular child, but trust that the child feels the way it does for a reason, and take that reason seriously. I don't know which way your grandson will go with any of this, and I don't have a hunch as to what to start with. You'll have to experiment, and these are some points of entry.