My son turned 5 this summer. Up til now I've always walked next to him well he rode and was able to run with him when he felt like going fast

Hes getting faster though and it feels like it's time for me to get a bike to ride with him

I know almost nothing about bikes. Haven't riden one in probably over 20 years

I was thinking just something used for now but I don't know what kind or brand I should be looking for

Can you guys help a brother out?

Trek or Specialized

Really, this depends on what you're thinking you're going to do with it.

If all you are going to do is ride around the block with your kid, then basically anything will do. Go to Goodwill or pick up a cheap cruiser from Walmart. (If you do go cheap, don't get something with gears. Cheap single-speed cruisers tend to work. Cheap geared mountain bikes tend... not to. Especially if assembled by idiots.)

This is contrary to most of what you will read here, because the people in this forum ride bikes. A lot. A long ways. And they tell you 'buy once, cry once'.

But I'm not talking to them. I'm talking to someone who hasn't been on a bike in 20 years and wants to ride with a 5 year old. You don't need a bike with a comma in the price tag. Black Friday yourself a Beach Cruiser from Walmart, and if you decide you want to 'get into' biking, then come back here and we'll give you advice on that.

Partially I speak here because I bought my now-ex Girlfriend a $1000+ dollar bike, only to see her basically never ride it, and never ever ride it farther than around the block a couple times with the kids (7 & 10). I should have bought her something cheaper, but I really hoped she'd go riding with me so I spent money. You sound like her, not me. I have multiple $1000+ dollar bikes and a Peloton... I use (or used) them all. But you sound like a buy cheap man.

Trek or Specialized!

QFT. Checkout Facebook Marketplace or OfferUp. You should be able to find something cheap to cruise around with your son. Then. If it gets more serious, you guys will figure out what the next move is.

This is awesome advice!

Watched Craigslist and such for a couple months.

Finally found a bike for a good price with the right frame size

Picked up a trek 700

Listing here

Took a bit to feel somewhat comfortable riding a bike again but I went for about 4 rides today with my son who just got his training wheels off 2 weeks ago. Good stuff

A couple things:

It's supposed to be a good city bike. My butt is really hurting after ride number 2. Will I get used to it or should I get another seat?

Are there any things I should consider doing to it to make it more enjoyable?

The front tire is getting bald in the center of tire. Didn't notice any major issues but should I replace or just ride til I have a problem?

Hopefully this makes sense. I'm really happy I was able to ride with my son, I just feel like there are some things I can do to make it more enjoyable

Thanks!

Your butt will hurt, no matter what saddle you use.  It just takes a little time to get used to being on a bicycle seat.

Definitely replace the tire ASAP.  You do not want to have a front tire go out on you while you are riding, especially if you son is within range of you and your bike crashing to the ground.  

Any time I've had a bike with a suspension seatpost, I replaced it.  They are heavy and don't contribute anything for me.   Just have to be sure and get the right size replacement and it will probably be $20 at a bike shop.

Most hybrid tires have a smooth center so it’s probably fine but, if they are several years old as those are I would probably replace them.
You could change the saddle to a wtb mountain bike saddle but it would cost 30% of what you paid for the bike. Ask at the bike shop and see what they have. The seat post doesn’t do much but again, what would it cost to replace.
Just ride the bike and decide what you want for your next bike. 😉

This is why I haven't asked a work-friend for bike purchase advice. I didn't know how deep she was into it until we were talking about her bike being stolen at a 2-day ride event. The replacement was $2500!

Is it too late to hijack OP's thread asking how to tell what frame size you need or general recommendations for an old fart with a mild girth issue?