Can bailiffs seize items that belong to my autistic son, like his iPad or his Nintendo Switch?

No

Bailiffs may only take control of goods that belong to the debtor.^[1]

An autistic person is a class of vulnerable people for the purpose of civil enforcement,^[2][3] and bailiffs may not recover fees and charges from vulnerable debtors until the debtor has been given adequate opportunity to get advice in relation to the enforcement power.^[4]

If the debtor is under 16, the bailiff may not take control of goods at all.^[5][6]

^{[1] Paragraph 10 of Schedule 12 of the Tribunals, Courts and Enforcement Act 2007
[2] Paragraph 77 of the Taking Control of Goods: National Standards 2014, April 2014
[3] See Bailiffs and vulnerable people
[4] Regulation 12 of the Taking Control of Goods (Fees) Regulations 2014
[5] Regulation 2 of the Taking Control of Goods Regulations 2013
[6] Regulation 10 of the Taking Control of Goods Regulations 2013}