Maksim Chmerkovskiy is home safe in the United States with his wife, Peta Murgatroyd, and their 5-year-old son, Shai, but a source tells ET that the couple now worries about «having to explain to their son what has been going on in the world and about where his dad was.»On Wednesday, Maksim returned to the States after fleeing Ukraine, where he is from, amid Russia's invasion, and was reunited with his family. «Peta is so thrilled to have Maks home and back with her and their son,» the source says. «She has been going through it and has been worried sick and emotional.»Peta is «so grateful» to have her husband back home as «it was a struggle for her and she spent a handful of nights crying herself to sleep,» the source notes.«She was doing her best to hide her somberness from their son because she didn't want him to internalize this or be scared,» the source adds.The source says of the alums, «Peta and Maks have received a ton of outpouring support from their friends and family.