Bacall's loss of her husband when her children were young does point to some of the issues surviving spouses face when there is a difference of age of 20 years or more. Of course, May-December marriages don't only happen in Hollywood, and the resources and circumstances can be very different.
In recent article titled "Bogie and Bacall: Iconic May-December romance", Market Watchdiscussed the estate planning issues that come up with marriages when one spouse is much older than the other.
Humphrey Bogart was 25 years older than Lauren Bacall when the two got married. At the time he was already a Hollywood legend while she was still a younger actress just coming into her prime. One obvious implication of this marriage is that she was likely to outlive him, which she did by a half century.
The biggest estate planning issue brought to attention by this Hollywood couple is that the younger spouse is likely to live much longer than the other. This creates issues of the older spouse possibly needing to provide assets for the surviving spouse and preserve an inheritance for any children. This is especially true if the older spouse has children from a previous marriage. The article lists a couple of ways that this issue can be handled, such as a QTIP trust, which provides for the inheritance to be used by the surviving spouse as long as he or she lives with the remainder going to the children. The article also suggests incorporating life insurance into the estate plan as another possibility.
These are not the only two ways to deal with this particular problem in May-December marriages. Estate planning attorneys have many other tools at their disposal that might be more appropriate in a given family situation. In Bacall's case, it appears that it did not matter too much. She left behind a large estate of her own and was able to provide for her children, grandchildren, and even her dog.
Reference: Market Watch (August 27, 2014) "Bogie and Bacall: Iconic May-December romance"