Boultham, hartsholme and nettleham parks. Daisymaid has an outdoor play area. Whisby nature reserve and garden centres have in and outdoor play areas (indoor ones cost) There's a couple of parks in North Hykeham too
Brant brougton, collingham, these are two that are a little out but we visit them often and always have a good time with the little ones x
Bassingham, skellingthorpe, nettleham bit further collingham is amazing