Hilo is a family-oriented town, and kids are welcome at most attractions and restaurants. Bear in mind, however, that facilities for diaper (nappy) changing and breastfeeding, as well as high chairs and other special equipment, are available only at major establishments.
Regarding accommodations, many B&Bs and inns don't allow children to stay due to potential noise and damage. Ask when booking to prevent any surprises. Also, if climbing stairs with a stroller is an issue, a hotel with an elevator might be preferable.
For young kids, Hilo's outdoor attractions, such as Onekahakaha Beach Park and Lili‘uokalani Park, are ideal. Older kids can appreciate the museums, which are brimming with info without being overwhelming: ‘Imiloa Astronomy Center of Hawai‘i is especially geared to curious grade-schoolers.