Objectives: In children, achieving an acceptable degree of accuracy from dietary or physical activity (PA) assessments remains a challenge. Children tend to overestimate their time spent in daily PA and underestimate their dietary intake of fat and sugar. Because parents play a key role in family lifestyle decisions, including children’s food choices and PA levels, it is important to investigate the responses of parents regarding their children’s lifestyle habits. We aimed to develop a Self-Administered Parental Assessment of Children’s Lifestyle (SAPLACL) questionnaire and test its feasibility and reliability in 191 parents (29 fathers and 162 mothers). Results: For each part of the questionnaire, the rate of missing or improper responses ranged from 0 to 24%. The highest proportion of problems in understanding was reported for the dietary intake dimension, especially for snacking in front of the TV. Some difficulty was also found regarding the question on leisure PA. Test–retest agreement was observed in 54.7–100% of the respondents. Overall, the kappa coefficients were favorable. Thus, the parent self-report questionnaire is a valid and accurate tool for analyzing children’s lifestyle habits in France.