This will not relate to confusion over the correct calculations, which will be perfectly understandable from the syntax and grammar of the text.
That is exactly the problem that children with developmental language disabilities have! They find the syntax and grammar really difficult to process at the best of times. Add in missing out words and other complications, and of course there is potential for confusion - unnecessarily.
You can phrase the questions to avoid dividing things between boys and girls, sure. Use year groups instead, or split a group into those who came by car or by foot, or whatever. You can use names that might be more gender neutral (but still easy to read), and use them in problems worded to avoid he/she if you must - Alex and Sam split £40 in the ratio 5:3 - how much does each child get?
But adding in complexities like 'they', that require the context, syntax, word order etc to get right - that is just taking the hardest things for a child with DLD and making them harder, for no beneficial reason.
You really aren't understanding the degree of language difficulty that some of the students have - and it's quite subtle in how it manifests, so it's often not apparent to the student or to the teacher exactly what's gone wrong or why. Sometimes I have thought that my pupils were really confused about some aspect of the maths, but it's only on very careful questioning that I have worked out that actually they have misinterpreted some part of the language of the question (often alongside a maths difficulty, which makes it even harder to work out). The children don't have normal knowledge of grammar and syntax, and if they struggle with maths as well, they aren't going to immediately predict what the examiner means because they are familiar with the type of maths questions.
There are plenty of ways of avoiding gendered language if you feel that is a real issue in maths exams - but things like using 'they' can really make life harder for language-disordered students.