“easier for them to handle” ?
You’re not deserting them, and if anything are doing them a favor by getting some much needed alone time with your spouse.
I don’t know what your situation is, but as a kid bubby coming to us to “babysit” was a lot of fun. You can tell them[use applicable names] “Mommy/Ima/Daddy/Abba/Tatte need to go take care of something(your mental health and relationship)and Savta will stay with you till we come back,”but with kids that young I don’t know if it will make a difference.enjoy your vacation!