Can I pay my 16-year-old son a wage for helping out in our family shop?

Yes, you can — but treat him exactly like any other employee, family or not. First, he needs to be past school leaving age to work those shifts; once he is, the child-employment hour caps fall away, though as a 16–17 year old he is still a "young worker" under the Working Time Regulations, so no more than 8 hours a day and 40 a week, with rest breaks and no night work. Pay him at least the National Minimum Wage: at 16 he sits in the under-18 band, which is £8.00 an hour from April 2026 (I checked the live GOV.UK rates — the 18–20 rate is £10.85 and 21+ is £12.71). If you aren't running payroll yet, register as an employer with HMRC and put him through PAYE like anyone else. Employee NICs apply from age 16 once earnings pass the threshold, and you'll owe employer NICs as usual. The wages are deductible as a business expense provided the work is genuine and the pay is commercial — keep proper records of hours and pay, because HMRC looks closely at family wages.