Hi
We were in Montenegro last summer. It is very safe there.
We stayed in Dobrota so not too far from Kotor. My husband did the walk up above Kotor to the castle walls (hard work in the heat) but worth it.
As previously mentioned the beaches around the fjord tend to be very shallow bits of beach/rocky jetties that get very busy. We preferred to go round the other side (bit more holidayish) as found Dobrota a bit residential. So places such as Stoliv and Prcanj (pronounced kind of perchan).
If you've got small children then somewhere that we went to a few times was UVALA PLOCE (near Budva). Doesn't look much in photos etc. but is quite nice there. It's a series of swimming/paddling pools over a hillside leading down to a beach. Great success with my toddler - restaurant to hand and my son went down to the beach.
Budva old town is nice for a wander around too. Also the Lovcen National Park is well worth a visit - stunning. Can't say I'd bother going to Centinje again though. It's a very long drive and not much there - a faded Venetian kind of sleepy Corfu type of town. The drive up the mountainside is well worth it for the views but the bit over to Centinje then takes a fair bit longer and not worth it in my opinion.
Perast is gorgeous - particularly nice to visit for an evening meal on a punta.
For proper beaches you need to head to the Adriatic coast (only about 15/20 mins drive really from Kotor).
An expensive but special restaurant not too far from Kotor is Stari Mlini near to Perast which is a fish specialist restaurant and is a stunning old building and surroundings. You sit in amongst small streams and ponds with your potential dinner swimming around you with views over the fjord.
A pleasant family restaurant with friendly service and traditional old stone decor etc. is Fork and Spoon (in Serbian Pirun i Ozica)which is in Dobrota.
Any other questions let me know.