Likely most 5 y/os once they realize you're friends with their parents will want to jabber at you themselves. Just talk to them about what they make it obvious they want to talk about at first. And don't talk in a baby voice, IE raise your voice up high and stuff-- They're little humans by that age.

Don't overthink it.

Kids have always loved me, had no idea why, not much love for them. Asked my ex-wife why they latch onto me when I often get annoyed with them.

"You talk to them like adults. You don't condescend and treat them like they're stupid, not afraid to use a strong vocabulary. No one else does that so they respond to the heightened respect."

I still use "big" words with them, but my own kids taught me to occasionally stop and ask, "Know what $X means?", then give a short answer and flow right back to where I was. In no case will I baby talk 'em, but you gotta realize, they'll pretend to understand a thing to keep the conversation going. They're having a blast being respected in such an unusual manner and don't want to derail the conversation.

As an example, don't say, "Oh! Do you like STAR WARS? It's really neato isn't it? When I was a little boy, I loved Star Wars! Isn't Darth Vader cool and scary?!"

Say instead, "Star Wars fan, huh? Seen Rogue One yet? That one jacked me up, wow. What did you think?" And then carry on (mostly) like you're shooting the shit with a friend.

(Hope that example comes across, it's not a thing I think about, just comes naturally.)

Kinda like how I learned to talk to girls in high school. Holy shit that turned out easy! Instead of treating them as beautiful, strange and untouchable creatures, putting them on a pedestal, talk to them just like your guy friends. With the other guys bumble fucking around trying to figure out what to say to be attractive and not offend, you really stand out.

Turns out people react well to be treated as equals. Who would have thought!

Ask them what they like, and then ask questions about that topic. Children are the easiest people to make friends with. They will be excited that you asked them anything about themselves, and if you continue to ask questions about what they like, they're going to adore you immediately.

I’m autistic and bad with kids, but this has worked with every one that age I’ve tried it with: ask them what they had for lunch, then what they’re going to have for dinner and then you can branch out to favorite foods and colors and movies and then it should go easily from there

Just talk with them like normal humans and pretend that you are a giant 5 year old.

As someone with a 5yo.

Sit on the floor when interacting with them. Literally being on their level can help a lot, that and talk about stuff they are into.

As someone else mentioned, don't baby talk to them, unless they have some specific learning disability, a 5yo will know a lot about what they are into (a dinosaur kid will know heaps about dinosaurs)

My boys all love Lego, build cool stuff, then let them have it, don't use instructions.

Aways come down to their height level when you talk to them so you can show them and read their facial non verbal language, you want to be on their same eye level but not on their face. Don't stare or make too intense eye contact.

Pick a topic and see how much enthusiasm the kid shows, that can be a useful clue to see if you re going the right way with your interaction. Take into account that some kids (and some adults too!) don't like interacting at all and that is also fine.

Some popular ones are: Dinosaurs, pets, tv shows/videogames, favorite color, favorite ice cream flavor, favorite song, favorite book.

Hope this helps.

They will inevitably ask you the age-old question of why...at that point you will go into the abyss of which there is no escape

Kids like attention. Ask them what they like to play, and what they like to watch. Talk to them like little adults and they generally will like that.

Get really hyped and stuff. Show them stuff. Play with them

Pull up in a white van with no or blackened windows and offer them candy. Oh and make sure "Free candy" is scratched in on the sides of the van. Wouldn't want people getting the wrong idea...

Now for the serious advice, don't do dumb jokes like the one above. Kids need honesty. Screwing around for shits and giggles is always a bad idea around them.

Kids often don't focus on the past or the future. Just the now. Don't ask them what they did on the weekend, they won't remember. Ask them dumb things like what fruit they like.

Get Duolingo for talking to children

Bring a board game or a pet.

Duolingo for talking to children

If you have access to Disney+ or piracy, watching a couple of (they're eight minutes long) episodes of the show Bluey would probably charm your butt off and also give you a lot to go on for fun ways to engage with kids.

It's all about being real and in the moment, and giving them ways to experience novelty. A parenting book my partner was reading reminded her that all you need to do to engage a (toddler, but the point stands) child's interest is to turn the laundry basket upside down. Everything that's dull to you is new to them (and everything that's exciting to you, they're often not ready for yet).

Be yourself, children will get past your facade and your inhibitions when you realise it.

I've sometimes behaved as if I don't give a shit and they still trigger me in the right direction to make me goofy.

Tbh, I don't. I don't like kids, and I will do anything I can to avoid interacting with them.

I’m a trans woman, so I just keep my head level, pretend I don’t see them, and just walk on by, lest some low-information voter think I’m a child molester and try to get me.

That said, children are absolute trash at paying attention to their destination and their environment, so when they inevitably cross my path in the dumbest possible way, I stop walking until they figure out they should go around me. That way I don’t accidentally kick the tiny knee-high humans.

I was one, once.