From my messenger inbox:
QuoteHello! Sorry to bother you. you may have such information. because on the Internet I can not find the answer to my question. Can I go to England with my son if he only has a birth certificate? (only I have a passport)
Child is 4 years old
No - BUT it's more complicated if he does not have one:
QuoteApplicants without passports must have their photograph and fingerprints taken at a VAC. Children under the age of 5 who do not hold a valid Ukrainian international passport will not have their fingerprints taken but will still need to book and attend a VAC appointment and have a digital photograph taken.
VACs in Ukraine are currently closed. There is a temporary VAC open in Rzeszow, Poland. Applicants must complete their online application and book an appointment before attending the Rzeszow VAC – walk-in appointments are no longer accepted. VACs are currently operating in European cities including Budapest, Chisinau, Warsaw, Bucharest and Paris.
See http://www.ukraineuk.info/lib/ukr_002.pdf