Contact a Family and the Lady Hoare Trust, which provide assistance and advice to children with disabilities and their families have merged under the Contact a Family name.
Discussion about a merger began two years ago when the trust approached Contact a Family. The trust decided its goals would be best met by merging with a UK-wide charity that shared its values, said Contact a Family chief executive Francine Bates.
Contact a Family receives substantial statutory funding - in October it received £1.5m for the next three years - and the Lady Hoare Trust receives a great deal of legacy funding.
Bates will be the chief executive, and all trustees will stay on board.
The trust's chief, Michael Ryan, will leave "amicably" and act as a consultant over the next three months, Bates said.