Please help

I have 4 kids my Oldest just turned 6 and my 2nd oldest will be 5 in August.

We live in an apartment, ground floor. My kids are friends with the neighbors and they love to play together.

The problem is my eldest 2 will sneak out of the house from morning and not come back until my husband gets back from work after 6pm and finds them and brings them inside.

I lock all the doors but they slip out between the bars on the balcony.

I have told them they can go outside in the afternoon and not to sneak out. They are not allowed out in the morning or in lunch time. And need to ask me first.

They do not listen! I have tried many different types of punishments but nothing works. I cant go outside and find them and knock on everyone's doors. I have to smaller children 3 and half and another who will be 2 in September.

They are safe we know the neighbors so it's not a matter of safety. It's a matter of them not listening.

When I see them outside out of the window I will call them to come back inside but they dont listen.

Please, If anyone has any advise I'd really appreciate it. I dont want any nasty comments so please dont leave any.

Just respond if you have any advice on how to get them to listen.

EDIT: Like I said my kids get punishments/consequences for the actions but nothing seems to work they still keep doing it.

I know they are at one of the neighbors houses we have 3 that they always go to. They are just playing with the kids not roaming around the streets.

We do not have a TV nor do my kids have tablets or any electronics they sometimes play or watch something on my phone but it's not often.

The door that opens onto the balcony is in my boys room it is a type of door that has no lock. There is a heavy wood blind they need to lift up to get out and they do that they slide out through the bars as the balcony door is locked.

My daughter says it's boring that's why she wants to always go out from morning instead of waiting until late afternoon. Which I can understand I'm bored too honestly but I dont drive my husband works 6days and long hours we are always home but I do not see that as an excuse for sneaking out and it's not acceptable but my punishments such as time outs, not getting treats my husband will bring ice cream or lollipops for the younger two but not them. At the time they cry n carry on and say they wont do it again but they just continue.

My kids were not like this a few months ago.