Summer in Denmark with children.

Do you plan to rent a car?

Sounds nice! Is there a question here?

Give Copenhagen 2-3 days. Then spend the time on Aero island or northern Zealand by the sea. Denmark is a wonderful beach.

Thank you. Yes , we will have a car. We would like to know recommended itenerary to staying. Prefer not to do too much traveling. 2 sites maybe 3 but a stay in the city and then seaside somewhere. Somewhere that has nice village and or culinary places
Appreciate your thoughts. Including specific areas and beaches.

Helsingør with Kronborg Castle and Swedish Helsingborg (20 minutes ferry) are one obvious destination imo.

Roskilde with Viking museum is a day trip or a stop.

Nykøbing on Falster with Medieval Center and close Knutenborg Safaripark might enjoy the kids.

Svendborg and Fåborg Sogn are famous yacht harbors in Fyn island, day trip Odense. Lykkesholm Slot offers nights in a rural palace.

Aarhus with Den Gamle By offers also modern architecture and excellent food places. The turbo ferry from Sealand makes it fun to get there. Fregatten Jylland in Ebeltoft is worth a visit for the kids.

Billund with Legoland you likely know already.

Ribe is the oldest town of Denmark and a pearl for history buffs.

Hi, You might check out Faxe Ladeplads on Zealand if you are renting a car. Smaller Marina/Beach town. Can be a little busy in the Summer with Danes spending time at the beach. (Nice sandy beach.) It's a bit of a drive from Copenhagen. Not a lot out that way but maybe it will appeal to you.
Have Fun !

If you're going to Copenhagen, having a car is a horrible idea. There are areas where a car makes sense, and there are areas where it doesn't. Use a car in the former areas and take the train in the latter.