The short answer is yes.
But, not for the reason you think it may have entered the public domain. Here's the long answer:
Because Hendrik van Loon wrote the majority of his books in America, and was from 1919 an American citizen, we need to apply US copyright law to see discover if his works are in public domain.
Before 1976 the system which operated in the USA was that for any work to gain copyright protection, it had to be registered with the Copyright Office. After registration, the initial period of protection was for 28 years and it could be renewed in the 28th year up to a total of 56 years. Usually the start date would be at or around the date of publication, but not always. Indeed sometimes authors and publishers forgot to register their works, or equally importantly, place a mandatory copyright notice on a work, and so such works would fall into the public domain almost immediately. The second thing which happened was that the renewal registration was frequently not carried out and so again the work might come into the public domain at that point.
With the coming into force of the 1976 Copyright Act the system changed to the one we had in the UK at the time, with copyright being based in the lifetime of the author plus, then, 50 years. Various arrangements were put into the Act to deal with those works which already existed under the old system. Anything which was published in the USA before 1923 automatically passed into the public domain, but the situation for works published between I January 1923 and 1 January 1964 was much more complicated and depended on whether a work was in its first 28 year registration period, and whether or not it had been re-registered. The Copyright Office have published guidance
(pdf) on how to navigate this complicated issue.
As van Loon's Story of the Bible
was published in 1923 it could have potentially come under the transitional arrangements, assuming that it had been correctly registered at the time of publication. However while it was correctly registered
in 1923 it appears not to have been re-registered and so fell into the public domain in 1952. This was well before the transitional arrangements might have extended the copyright term to 2018, had it been re-registered. You can even download the book in digital format for free by using the links on the right hand side of the registration entry shown above.