One-fifth of all disabled children have mobility limitations. Early provision of powered mobility for very young children (aged 5 years) is hypothesised to trigger positive developmental changes. However, the optimum age at which to introduce powered mobility is unknown.The aim of this project was to synthesise existing evidence regarding the effectiveness and cost-effectiveness of powered mobility for very young children, compared with the more common practice of powered mobility provision from the age of 5 years.The study was planned as a mixed-methods evidence synthesis and economic modelling study. First, evidence relating to the effectiveness, cost-effectiveness, acceptability, feasibility and anticipated outcomes of paediatric powered mobility interventions was reviewed. A convergent mixed-methods evidence synthesis was undertaken using framework synthesis, and a separate qualitative evidence synthesis was undertaken using thematic synthesis. The two syntheses were subsequently compared and contrasted to develop a logic model for evaluating the outcomes of powered mobility interventions for children. Because there were insufficient published data, it was not possible to develop a robust economic model. Instead, a budget impact analysis was conducted to estimate the cost of increased powered mobility provision for very young children, using cost data from publicly available sources.A range of bibliographic databases [Cumulative Index to Nursing and Allied Health Literature (CINHAL), MEDLINE, EMBASE™ (Elsevier, Amsterdam, the Netherlands), Physiotherapy Evidence Database (PEDro), Occupational Therapy Systematic Evaluation of Evidence (OTseeker), Applied Social Sciences Index and Abstracts (ASSIA), PsycINFO, Science Citation Index (SCI; Clarivate Analytics, Philadelphia, PA, USA), Social Sciences Citation Index™ (SSCI; Clarivate Analytics), Conference Proceedings Citation Index - Science (CPCI-S; Clarivate Analytics), Conference Proceedings Citation Index - Social ScienceHumanities (CPCI-SSH; Clarivate Analytics), Cochrane Central Register of Controlled Trials (CENTRAL), Cochrane Database of Systematic Reviews, Database of Abstracts of Reviews of Effects (DARE), NHS Economic Evaluation Database (NHS EED), Health Technology Assessment (HTA) Database and OpenGrey] was systematically searched and the included studies were quality appraised. Searches were carried out in June 2018 and updated in October 2019. The date ranges searched covered from 1946 to September 2019.In total, 89 studies were included in the review. Only two randomised controlled trials were identified. The overall quality of the evidence was low. No conclusive evidence was found about the effectiveness or cost-effectiveness of powered mobility in children aged either 5 or ≥ 5 years. However, strong support was found that powered mobility interventions have a positive impact on children's movement and mobility, and moderate support was found for the impact on children's participation, play and social interactions and on the safety outcome of accidents and pain. 'Fit' between the child, the equipment and the environment was found to be important, as were the outcomes related to a child's independence, freedom and self-expression. The evidence supported two distinct conceptualisations of the primary powered mobility outcome, movement and mobility: the former is 'movement for movement's sake' and the latter destination-focused mobility. Powered mobility should be focused on 'movement for movement's sake' in the first instance. From the budget impact analysis, it was estimated that, annually, the NHS spends £1.89M on the provision of powered mobility for very young children, which is 2% of total wheelchair service expenditure.The original research question could not be answered because there was a lack of appropriately powered published research.Early powered mobility is likely to have multiple benefits for very young children, despite the lack of robust evidence to demonstrate this. Age is not the key factor; instead, the focus should be on providing developmentally appropriate interventions and focusing on 'movement for movement's sake'.Future research should focus on developing, implementing, evaluating and comparing different approaches to early powered mobility.This study is registered as PROSPERO CRD42018096449.This project was funded by the National Institute for Health Research (NIHR) Health Technology programme and will be published in full inThe aim of this study was to find out the benefits and costs of providing very young children, aged 5 years, with powered mobility devices. Examples of powered mobility devices are electrically powered wheelchairs and modified ride-on toys. We looked at many research papers about children and powered mobility. We found many benefits of powered mobility. We then combined all of the information to see if using powered mobility before the age of 5 years had any specific benefits for children. The evidence tells us that powered mobility has a positive effect on children’s movement, and it can boost children’s social interactions with other people, and their independence. Children using powered mobility were able to go to their friends by themselves, move around a play space as they wanted and take part in physical activities and games. We found that the fit between the child, the powered mobility device and the child’s everyday environment was important. When the fit was not good, children experienced a lot of problems. Some children and families felt that powered mobility did not suit their needs, leading to children using a manual wheelchair instead and thereby missing out on education, social opportunities and play. Barriers to powered mobility were found in the physical environment (e.g. inaccessible buildings) and the social environment (e.g. adults supervising children too closely) and often affected children’s independence. We found that the advantages and disadvantages of powered mobility were similar in younger and older children, even though the activities they took part in were different. We also found that each year the NHS spends 2% of its wheelchair service budget on powered mobility for very young children. In conclusion, powered mobility can benefit very young children, but it requires a good fit with the child’s environment.