my 17month old refuses to sit on grass or sand.. he completely freaks out when he's put down on it by screaming, crying and trying to climb up me, i've tried engaging him in many interesting things and taking his favorite food and trying to have a picnic but it's not helping..he won't even sit on it when a blanket is separating him from the grass or sand.... even though it's embarrassing, i'm more worried that at this age he's still not getting used to....i could really do with any tips anyone might have..as i've tried many tricks divert his attention but it's not working....

thanks