ELvis,
I've done various holidays in Norway; the first was either a June or July when I was pregnant and it was unusually warm and sunny (Bergen can make Manchester seem dry, and before I get slated for that I'm an ex-Mancunian !) I was staying with friends who had 2 school age kids and a new baby. We visited the Bergen aquarium (accessible with a pram), and various local lakes for swimming and walks.
The next trip, again to Bergen was when my dd was 9 months old; This time we'd gone over for the Norwegian national day on 17th May and the weather was distinctly damp ! But we still managed to go up a mountain on the funacular (sp ?) railway (another favourite with their kids) then walked around a nature trail and had a picnic.
We've also been in the depths of winter when dd was just over 2. We stayed in the mountains in a village called Hemsedahl (about 5 hours drive from Bergen) which is a very popular summer venue as well as for winter skiing. Lots of bike routes, walks, and picture postcard scenery. Geilo is supposed to be another good mountain place to go, and closer to the Western side, I think there's a glacier there.
We've always flown and then hired a car. There are direct flights to Bergen from Gatwick and Stanstead with Brathaans (who I think have just been taken over by SAS) also to Stavanger.
If you take your own car, be aware that you have to use dipped headlights at all times, speed limits are in kilometres even though the numbers are similar to ours - eg max limit on most roads is 60 kph !! So progress is quite slow and speed cameras are as common as they are here, even in the mountains
Finally, if you like a drink and want to make your holiday money spin out then make the most of your outbound duty-free allowance. Wine and spirits are only available at state owned bottle shops and prices are sky-high ! Beer is available in supermarkets but again is pricy.