If you like coffee shops and restaurants that are child friendly look at Springfields. It is an outlet place but has lovely gardens that are free. At the back is a sensory garden and little motorised boat lake that children can play with.Ducks are everywhere and it is an excellent place for them to run a bit of energy off. Also Baytree at Christmas time has a lovely Grotto. It really is fabulous for little ones.
Other ideas that are helpful with small children-
There is an arts centre that has all sorts of creative workshops too.
Next to Baytree there is a ball pit play place (and a taser place for when they are older). In town there is an bowling alley and indoor swimming pool.
There is also a water taxi that takes you from town into Springfields which my children loved.
There is an aviary and children playground in the grounds of Ayscoughfee which is a also a free museum with events for children.
Before I forget there is also a lovely independent bookshop in the town called Bookmark with a cafe.
The children's park at Surfleet is wonderful too and the Mermaid pub at Surfleet is excellent.
Dyke pub outside of Bourne is worth a visit.
When we moved up we were looking for a house in either Bourne or Spalding as my DH was working in one of the Grammar schools. We asked around and we were advised to avoid the new build housing estates at Bourne (one of the school governors with connections) and that Spalding had more to offer a young family. Having lived there for a decade I would say that is true.
Grantham is a fine as long as you live in one of the outlying villages but that comes with it's own restrictions.
Anyway-good luck with everything 🙂