The place is totally suitable for kids, or for some people nostalgic about Lego, such as me. My visit of the museum bought some memories, but there were also some Lego series that are new to me.
There are some bigger and more complex Lego figures both inside and outside parts of the museum. I can imagine that the outside yard must be very interesting for kids, especially in summer, since there are possibilities to play ball sports. For adults, the yard offers a café, that I assume is open in summer. I visited the place in November and the café was closed.
I find the placement of all texts about the original and history of the Lego a bit unfortunate. First of all, it's not very clear which text should be read after which one, and secondly, the space of the stairs is a bit narrow so you need to step back to be actually able to read anything. The stairs might be packed like that. At the same time, I understand that there is a lot of Lego showpieces and that everything is a bit squeezed in one house.
Unless you or your kids are totally into Lego, and unless you aim to read all the information at the stairs, the visit of the museum lasts about 1 hour.